BACKGROUND OF THE INVENTION 
     Neurosurgery routinely involves performing craniotomies for exposure of the brain and intracranial contents for various intracranial pathologies including tumors, head injuries, vascular malformations, aneurysms, infections, hemorrhages, strokes, and brain swelling. A craniotomy involves creation of burr holes and removal of a portion of the skull (bone flap) with subsequent approximation of the bone flap for closure. Several methods and fixation devices are available for re-attaching the bone flap to the skull including small metallic or absorbable plates with screws or wires. Another method has been the use of cranial clamps consisting of two connected circular elements placed on the inside and outside surfaces of the skull. All of the aforementioned cranial fixation devices in the prior art provide for a rigid fixation of the bone flap to the skull. 
     In cases of post-operative intracranial hemorrhage and/or brain swelling development, a decompressive craniectomy is performed. Decompressive craniectomy is a neurosurgical procedure used to treat increased intracranial pressure (ICP) from head injury, stroke, brain tumor, infection, cerebral hemorrhage, and space occupying lesions. The technique involves removal of the skull and opening of the dura mater covering the brain, thereby allowing the swollen brain to herniate outwards through the surgical skull defect rather than downwards to compress the brainstem. The procedure improves outcomes by lowering ICP, the pressure within the skull. Increased ICP is very often debilitating or fatal because it causes compression of the brain and restricts cerebral blood flow. The aim of decompressive craniectomy is to reduce this pressure. The larger the removed bone-flap is, the more ICP is reduced. Following removal of the bone flap, the dural opening is closed with a patch graft taken from a cow, pig, cadaver, or a synthetic graft. The preferred method is a synthetic collagen matrix since it is capable of expanding. In addition to reducing ICP, studies have found decompressive craniectomy to improve cerebral perfusion pressure and cerebral blood flow in head injured patients. 
     Decompressive craniectomy is used to treat major strokes associated with malignant brain swelling and increased ICP. It is well known that a decompressive craniectomy improves survival and functional outcome in patients with severe brain swelling from head injury or stroke if performed in a timely manner. There usually is an inherent time delay between diagnosing the cause of the increased intracranial pressure and performing the decompressive craniectomy. Typically, once a post-operative increase in ICP is detected, either through a clinical exam or an ICP monitoring device, medical treatment is initiated and a CT or MRI imaging is obtained to identify the underlying cause of the raised intracranial pressure. If the need for a re-operation or decompressive craniectomy is identified, the anesthesiologist and operating room staff are notified and the surgery is subsequently undertaken. Unfortunately, at times the operating room and/or staff are at full capacity necessitating further delay until the surgery can be performed. Despite the best of attempts by the surgeon, in cases of massive brain swelling or a rapidly developing post-operative hemorrhage, the patient may end up with irreversible brainstem injury with consequent vegetative state or death. 
     After a craniectomy, the risk of brain injury is increased because of the removed bone flap, particularly after the patient heals and becomes mobile again. Therefore, special measures must be taken to protect the brain, such as a helmet or a temporary implant in the skull. 
     When the patient has healed sufficiently, the craniectomy skull defect is usually closed with a cranioplasty. Cranioplasty is repair of a defect in the vault of the skull. This repair can be carried out by using bone removed at earlier surgery that has been preserved or by using bone from elsewhere as a graft. The iliac bone bounding the pelvis, ribs and even a part of adjacent skull bone can be used. If possible, the original bone flap is preserved after the craniectomy in anticipation of the cranioplasty. The bone flap is usually stored sterilely in a freezer until the patient is ready for implantation of the bone flap into the craniectomy skull defect. Typically, this time period can last several months since it may take this long to treat the underlying cause of the increased intracranial pressure. This extended time period not only increases the risk of brain injury but also increases the risk of infection in the stored bone flap. Another technique of storing the removed bone flap involves placing it under the skin in the abdomen. This requires a surgical procedure to place the bone flap in the abdomen and another one to remove it, thereby also increasing the consequent risks to the patient. In cases where the bone flap cannot be replaced due to infection or any other reason, the skull defect is repaired either with a prosthetic plate or a titanium mesh and bone cement. A prosthesis obviously cannot completely replicate the original skull defect and therefore, some cosmetic deformity persists following a prosthetic cranioplasty. The prosthesis also increases the risk of infection. 
     The risks associated with cranioplasty include infection, hemorrhage, brain injury, seizures, and death along with other risks inherent to any surgery and general anesthesia. It is also usually necessary for the patient to be in hospital for a week or so after a cranioplasty. 
     U.S. Pat. No. 5,902,304 to Walker et al. describes a telescopic bone plate for use in bone lengthening by distraction osteogenesis. The bone plates are attached to osteomically separated mandible or skull sections connected by a thread screw assembly. The extent of the required distraction can be adjusted by an external screwdriver. U.S. Pat. No. 5,993,448 to Daniel J. Remmler describes a skull fixation device for treatment of craniofacial deformities that provides for relative movement of the skull segments by a percutaneously placed external wrench. U.S. Pat. No. 6,187,004 to Jeffrey A. Fearon describes a mandible or skull expansion plate. The extent of the expansion is adjusted by an externally placed device. 
     The aforementioned cranial fixation devices in the prior art provide for treatment of craniofacial defects in particular craniosynostosis. They all require an external screwdriver to control the extent of the skull movement allowed and they do not describe or provide for outward or inward movement of the both flap relative to the skull in response to a change in the intracranial pressure. 
     U.S. patent application No. 60/812,105 to Kathryn Ko describes a method of performing decompressive craniectomy with the bone flap attached to the skull with a hinged plate. The method describes attaching the hinged plate to one end of the bone flap and a rigid plate to the other end. The described method also requires a re-operation to fixate the unconstrained bone flap at the rigid plate end to the skull. U.S. patent application Ser. No. 12/033,815 to Tucci also describes a method similar to the Ko application of attaching the bone flap to the skull with a hinged plate at one end of the bone flap and a straight plate at the other end with unconstrained bone flap movement. They also describe a deformable plate which could be used instead of a hinged plate for bone flap attachment. This construct would also require a re-operation to fixate the unconstrained bone flap at the straight plate end. Tucci also describes a two part sliding device for cranial fixation. The device is not very practical as it very significantly sticks outwards from the skull surface and has a very high profile and obvious painful cosmetic defect with overlying skin irritation and risk of erosion/infection. This device would also require another operation to remove it once the bone flap approximates to the skull. 
     Considering the aforementioned complexities and risks involved in the post-operative management of critically ill patients undergoing a craniotomy, there is a need for a better technique which provides for cranial fixation along with immediate treatment of increased intracranial pressure and avoids the need for performing a subsequent cranioplasty. 
     SUMMARY OF THE INVENTION 
     The present invention relates to a cranial fixation device for fixing a bone flap to the skull following a craniotomy. It also provides for constrained outward movement of the bone flap to immediately accommodate for an increase in intracranial pressure and subsequently allowing for the bone flap to move inwards up to the skull once the intracranial pressure normalizes. 
     In one embodiment, the cranial fixation device comprises of a plate that attaches to the skull and bone flap. The plates are attached to the skull with telescopic screws and the bone flap with regular screws. The telescopic screws allow outward movement of the bone flap as well as inward movement of the bone flap up to the skull level. The plate does not allow the bone flap to move inward inside the cranium below the skull level. 
     In another embodiment, the cranial fixation device comprises a plate that attaches to the skull and bone flap with bone fasteners. The bone fasteners attached to the skull are telescopic and bone fasteners attached to the bone flap are regular screws. The telescopic bone fasteners also comprise a locking mechanism that engages when the telescopic bone fastener is in a retracted position. The retracted telescopic bone position approximates the bone flap to the skull when the intracranial pressure is in the normal range. With an increase in ICP, the pressure placed on the bone flap disengages the telescopic bone fastener locking mechanism and allows outward movement of the bone flap to accommodate the increase in ICP and subsequently allowing the bone flap to retract back to the skull level once the ICP normalizes. The telescopic screw locking mechanism comprises of one or more collapsible balls mounted on one telescopic extension with corresponding sockets on the said second telescopic component. Other locking mechanisms include ratchet teeth, ratchet teeth and pawl mechanism, collapsible ratchet teeth, threads, and ridges with notches. Several locking mechanisms are described here forth. In one embodiment of the telescopic screw, the locking mechanism comprises a ridge in the telescopic extension with a corresponding socket along the axial and longitudinal axis of the screw wall. In another embodiment of the telescopic screw, the locking mechanism comprises of ridges in the telescopic extension with notches in the inner screw wall. In another embodiment of the telescopic screw, the locking mechanism comprises of ratchet teeth in the telescopic extension and inner screw wall. In another embodiment of the telescopic screw, the locking mechanism comprises of ratchet teeth in the telescopic extension with a pawl in the inner screw wall. The ratchet teeth can be unidirectional or bidirectional. In another embodiment of the telescopic screw, the locking mechanism comprises of collapsible ratchet teeth in the telescopic extension with an engaging defect or ratchet teeth in the inner screw wall. In another embodiment of the telescopic screw, the locking mechanism comprises of threads in the telescopic extension and the inner screw wall. In another embodiment of the telescopic screw, the locking mechanism comprises of a spring. The spring loaded telescopic screw places the screw in a retracted position once the intracranial pressure normalizes and positions the bone flap in proximity to the skull. 
     Rather than providing a fixed locked position once implanted as described in all the cranial fixation devices in the prior art, the current invention allows for constrained outward movement of the bone flap relative to the skull in cases of cerebral swelling and subsequently retracts the bone flap against the skull once the swelling subsides. 
     In the various embodiments described herein the preferred plate configuration is circular so as to cover the burr hole or skull opening. Other plate configurations could be rectangular, square, straight, X-shaped, Y-shaped, fan shaped, or any other configuration able to connect the skull to the bone flap. Similarly, the telescopic configurations described are either cylindrical or rectangular and designed to fit into the hollow screw. Other telescopic configurations could be partially solid, tapered, V-shaped or any other configuration that fit&#39;s the screw opening. The plate and screws can be made of titanium or titanium alloy for MRI imaging compatibility. They could also be made of a bio-absorbable material (polyesters, poly amino acids, polyanhydrides, polyorthoesters, polyurethanes, polycarbonates, homopolymers, copolymers of poly lactic acid and poly glycolic acid, copolyesters of e-caprolactone, trimethylene carbonate, and para-dioxanone), or allograft or xenograft bone that is absorbed by the body over time once the bone flap has fused with the skull. Alternatively, it could made of a radiolucent material (polyetheretherketone), plastic, or a combination of plastic and metal to reduce CT and MRI imaging artifact. 
     Although the application for the cranial fixation device described in the various embodiments is for fixation of the bone flap to the skull following a craniotomy, it can also be used to cover a burr hole or skull fracture. Other applications include treatment of increased intracranial pressure following traumatic injury, subdural hemorrhage, epidural hemorrhage, subarachnoid hemorrhage, intra-ventricular hemorrhage, brain hemorrhage, ischemic stroke, hemorrhagic stroke, hypoxia, tumor, infection, brain swelling, and/or seizure. The plate and screw construct not only approximate the bone flap to the skull but can also allow external movement of the bone flap relative to the skull in case of an increased intracranial pressure. The external movement of the bone flap increases the intracranial space to accommodate the increase in intracranial pressure and provides for a decompressive craniectomy. Following normalization of the intracranial pressure, the bone flap retracts back towards the skull. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional side view of one embodiment of the telescopic screw in a retracted position. 
         FIG. 2  is a cross-sectional side view of the screw in  FIG. 1  shown in an extended position. 
         FIG. 3  is a cross-sectional side view of another embodiment of the telescopic screw in a retracted position. 
         FIG. 4  is a cross-sectional side view of the screw in  FIG. 3  shown in an extended position. 
         FIG. 5  is a cross-sectional side view of another embodiment of the telescopic screw in a retracted position. 
         FIG. 6  is a cross-sectional side view of the screw in  FIG. 5  shown in an extended position along with the plate. 
         FIG. 7  is a cross-sectional side view of the screw seen in  FIG. 6  with another embodiment of the plate. 
         FIG. 8  is a cross-sectional side view of another embodiment of the telescopic screw in a retracted position. 
         FIG. 9  is a cross-sectional side view of the screw in  FIG. 8  shown in an extended position along with the plate. 
         FIG. 10  is a cross-sectional side view of the screw seen in  FIG. 9  with another embodiment of the plate. 
         FIG. 11  is a cross-sectional side view of another embodiment of the telescopic screw in a retracted position. 
         FIG. 12  is a cross-sectional side view of the screw in  FIG. 11  shown in an extended position. 
         FIG. 13  is a cross-sectional side view of another embodiment of the telescopic screw in a retracted position. 
         FIG. 14  is a cross-sectional side view of the screw in  FIG. 13  shown in an extended position. 
         FIG. 15   FIG. 11  is a cross-sectional side view of another embodiment of the telescopic screw in a retracted position. 
         FIG. 16  is a cross-sectional side view of the screw in  FIG. 15  shown in an extended position. 
         FIG. 17  is a cross-sectional side view of another embodiment of the telescopic screw in a retracted position. 
         FIG. 18  is a cross-sectional side view of the screw in  FIG. 17  shown in an extended position. 
         FIG. 19  is a cross-sectional side view of another embodiment of the telescopic screw in a retracted position. 
         FIG. 20  is a cross-sectional side view of the screw in  FIG. 19  shown in a partially extended position. 
         FIG. 21  is a top view of the screw head. 
         FIG. 22  is a cross-sectional view of the screw in  FIG. 19  shown in a completely extended position. 
         FIG. 23  is a cross-sectional side view of another embodiment of the telescopic screw in a retracted position. 
         FIG. 24  is another cross-sectional side view of the screw in  FIG. 23 . 
         FIG. 25  is a cross-sectional side view of the screw in  FIG. 24  shown in an extended position. 
         FIG. 26  is a cross-sectional side view of another embodiment of the telescopic screw in a retracted position. 
         FIG. 27  is a cross-sectional side view of the screw in  FIG. 26  shown in an extended position. 
         FIG. 28  is a cross-sectional side view of another embodiment of the telescopic screw in a retracted position. 
         FIG. 29  is another cross-sectional side view of the screw in  FIG. 28 . 
         FIG. 30  is a cross-sectional side view of the screw in  FIG. 29  shown in a partially extended position. 
         FIG. 31  is a cross-sectional side view of the screw in  FIG. 29  shown in a completely extended position. 
         FIG. 32  is a top view of another embodiment of the screw head. 
         FIG. 33  is a cross-sectional side view of another embodiment of the telescopic screw in a retracted position. 
         FIG. 34  is a cross-sectional side view of the screw in  FIG. 33  shown in a partially extended position. 
         FIG. 35  is a cross-sectional side view of the screw in  FIG. 33  shown in a completely extended position. 
         FIG. 36  is a side view of the screw driver used to place the screw shown in FIG.  33 . 
         FIG. 37  is a cross-sectional side view of another embodiment of the telescopic screw in a retracted position. 
         FIG. 38  is a cross-sectional side view of the screw in  FIG. 37  shown in a partially extended position. 
         FIG. 39  is a cross-sectional side view of the screw in  FIG. 37  shown in a completely extended position. 
         FIG. 40  is a cross-sectional side view of another embodiment of the telescopic screw in a retracted position. 
         FIG. 41  is a top view of the screw shown in  FIG. 40   
         FIG. 42  is a cross-sectional side view of the screw in  FIG. 40  shown in a partially extended position. 
         FIG. 43  is a cross-sectional side view of the screw in  FIG. 40  shown in a completely extended position. 
         FIG. 44  is a side view of the screw driver used for placement of the screw shown in  FIG. 40 . 
         FIG. 45  is a top view of one embodiment of the cranial fixation plate. 
         FIG. 47  is a top view of another embodiment of the cranial fixation plate. 
         FIG. 48  is a top view of another embodiment of the cranial fixation plate. 
         FIG. 49  is a top view of another embodiment of the cranial fixation plate. 
         FIG. 50  is a top view of another embodiment of the cranial fixation plate. 
         FIG. 51  is side plan view of one embodiment of the cranial plate attached to the bone flap and skull with the telescopic screw in a retracted position. 
         FIG. 52  is a side plan view of the plate in  FIG. 51  with the telescopic screw in a partially extended position. 
         FIG. 53  is a side plan view of the plate in  FIG. 51  with the telescopic screw in a completely extended position. 
         FIG. 54  is a partial cross-sectional side view of the skull and brain. 
         FIG. 55  is partial cross-sectional side view of the skull and brain. 
         FIG. 56  is a partial cross-sectional side view of the skull and brain. 
         FIG. 57  is a partial cross-sectional side view of the skull and brain. 
         FIG. 58  is a partial cross-sectional side view of the skull and brain. 
         FIG. 59  is a partial cross-sectional side view of the skull and brain with cranial fixation plates and screws in place. 
         FIG. 60  is a partial cross-sectional side view of the skull and brain with cranial fixation plates and screws in place. 
         FIG. 61  is a side view of another embodiment of the telescopic extension. 
         FIG. 62  is another side view of the telescopic extension seen in  FIG. 61 . 
         FIG. 63  is a cross-sectional side view of a telescopic housing member with the telescopic extension seen in  FIG. 62  positioned outside the housing member. 
         FIG. 64  is a cross-sectional side view of a telescopic housing member with the telescopic extension seen in  FIG. 62  positioned inside the housing member. 
         FIG. 65  is a cross-sectional side view of a telescopic housing member with the telescopic extension seen in  FIG. 61  in a completely retracted position. 
         FIG. 66  is a partial cross-sectional side view of another embodiment of the telescopic screw. 
         FIG. 67  is a partial cross-sectional side view of the screw in  FIG. 67  in a retracted position. 
         FIG. 68  is a partial cross-sectional view of the screw in  FIG. 67  in an extended position. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIGS. 1 and 2  illustrate a telescopic screw with a housing component  1  and a telescopic component  2 . The telescopic component at one end has a head with a recess  4  and a widened portion  3  and at the other end has extensions  5 . The telescopic component  2  is contained inside the housing component  1 . The housing component has extensions  6  and a recess  8 . The screw is drilled into the skull with a screwdriver attached to the recess  4 .  FIG. 1  illustrates the telescopic screw in a retracted position with the wider head portion  3  engaged with the recess  8  to provide a locking mechanism.  FIG. 2  illustrates the screw placed in an extended position by an increase in the intracranial pressure. The telescopic component extension  5  and the housing component extension  6  prevent the telescopic component from pulling out from the housing component during a maximally extended position. 
       FIGS. 3 and 4  illustrate another embodiment of the telescopic screw. The telescopic component  10  has an extension  11  and the housing component  9  has a recess  12  at the screw tip end. As shown in  FIG. 3  with the screw in a retracted position, the extension  11  and recess  12  are engaged and provide a locking mechanism.  FIG. 4  illustrates the screw in an extended position. 
       FIGS. 5-7  illustrate another embodiment of the telescopic screw with a housing component  13  and a telescopic component  14 . The telescopic component at one end has a head  17  with a recess  18  and at the other end has extensions  15 . The telescopic component  14  is contained inside the housing component  13 . The screw is drilled into the skull with a screwdriver attached to the recess  18 .  FIG. 5  illustrates the telescopic screw in a retracted position and  FIG. 6  illustrates the screw placed in an extended position by the plate  19 . The screw is placed through the plate hole  20 . The plate  19  is attached to the skull and bone flap and a rise in the intracranial pressure forces the plate to move outwards with the bone flap, thereby placing the telescopic screw in an extended position.  FIG. 7  illustrates the plate  21  with a recess  22  which provides a lower profile for the screw head and decreases the overlying skin irritation. 
       FIGS. 8-10  illustrate another embodiment of the telescopic screw with a housing component  23  and a telescopic component  24 . The telescopic component at one end has a head  25  and extensions  26 . The housing component has extensions  28  and recess  29 . In a retracted position as shown in  FIG. 8 , the head extension  26  engages with the housing component recess  29 .  FIG. 9  illustrates with screw in an extended position with the plate  27  and  FIG. 10  illustrates the screw in an extended position with a lower profile plate  31  with a thinner screw head engaging portion  30 . 
       FIGS. 11 and 12  illustrate another embodiment of the locking mechanism for the telescopic screw with a housing component  32  and a telescopic component  33 . The housing component comprises recesses  35  and  36  that engage with the extension  34  of the telescopic component  33 .  FIG. 11  shows the screw in a retracted position with the extension  34  engaged with the recess  36  and  FIG. 12  illustrates an extended position of the screw. 
       FIGS. 13 and 14  illustrate another embodiment of the locking mechanism for the telescopic screw. The housing component  38  contains a collapsible ratchet  39  that engages with the recess  40  in the telescopic component  37 .  FIG. 13  shows the screw in a retracted position with the ratchet tooth  39  engaged with the recess  40  and  FIG. 14  shows the telescopic component in an extended position with the ratchet  39  collapsed back towards the housing component wall  38 . 
       FIGS. 15 and 16  illustrate another embodiment of the locking mechanism for the telescopic screw. The housing component  41  contains a collapsible ball/spring  43  near the head of the screw that engages with the recess  44  on the telescopic component  42 .  FIG. 15  shows the screw in a retracted position with the ball  43  engaged with the recess  44  and  FIG. 16  illustrates the screw in an extended position. In other embodiments the telescopic components can contain recesses in partially and completely extended screw positions also. 
       FIGS. 17 and 18  illustrate another embodiment of the locking mechanism for the telescopic screw. The housing component contains a collapsible extension  47 . The telescopic component  46  contains an extension  48  which engages with extension  47  and locks the telescopic component in the retracted position.  FIG. 18  shows the locking mechanism disengaged with the screw in an extended position. 
       FIGS. 19-22  illustrate another embodiment of the telescopic screw containing a housing component  49 , a telescopic component  50  with a head  51  and an intermediate telescopic component  54 . The head  51  contains a recess  52  for the screw driver at one end and an extension  58  at the other end. The intermediate telescopic component contains an extension  56  on the outside and a recess  57  inside. The housing component comprises of an extension  53  which engages with the extension  56  and prevents the intermediate extension from pulling out in an extended position as shown in  FIG. 20 .  FIG. 19  illustrates the retracted position of the screw with telescopic portion  50  extension  58  engaged with the recess  57  in the intermediate portion  54  and the intermediate portion extension  56  engaged with the recess  55  in the housing component.  FIG. 20  illustrates the partially extended position of the screw.  FIG. 21  shows the top view of the screw head  51  with a recess  52  for the screwdriver.  FIG. 22  illustrates the screw in a completely extended position. 
       FIGS. 23-25  illustrate another embodiment of the telescopic screw with a housing component  61  with a screw head  62  and a telescopic component  60  and a head  59 . The housing component  61  contains a central portion  65  with an extension  67 . The telescopic component contains arms  64  with extensions  66  at the ends. The telescopic portion head  59  also contains a recess  63  for the screwdriver.  FIGS. 23 and 24  illustrate the screw in a retracted position and  FIG. 25  shows the screw in an extended position. The extension  67  engages with the extension  66  and prevents the telescopic component  64  from pulling out from the housing component  61 . 
       FIGS. 26 and 27  illustrate another embodiment of the screw with a telescopic component with a head  68  and extension arms  73  and  76  which each contain a wider portion  75  at the proximal end and an extension  74  at the distal end. The housing component  70  contains the screw tip  71  at one end and extensions  72  at the other end. The telescopic screw head  68  contains a recess  69  for the screwdriver. The wider portion  75  of the telescopic component arms engages with the extension  72  on the housing component and locks the screw in a retracted position as illustrated in  FIG. 26 .  FIG. 27  illustrates the screw in an extended position. In other embodiments the telescopic component arms  73  and  76  can be manually compressed against each other and placed after the housing component is implanted into the skull bone. 
       FIGS. 28-31  illustrate another embodiment of the telescopic screw with a housing component  78  with screw tip  79  and a telescopic component with a head  76  and body  77  as shown in  FIG. 28 . The telescopic component contains extension arms  81  with extension  83  at the distal end of the arms. The housing member also contains a central extension  85  with a widened tip  86 . The screw also contains an intermediate telescopic component  82  with a head extension  84  at one end on the outside and a recess  88  on the inside as well as an extension  87  at the other end.  FIG. 29  shows the screw in a retracted position.  FIG. 30  shows the screw in a partially extended position with the telescopic component  81  in an extended position and intermediate component  82  in a retracted position. The extension  83  engages with the head  84  and prevents the telescopic component  81  from pulling out. The housing component central extension  85  widened tip  86  engages with the recess  88  in the intermediate telescopic component  82  during the retracted position.  FIG. 31  illustrates the screw in a completely extended position. The telescopic component  81  extensions  83  engage with the intermediate component  82  head  84  and the housing component extension  85  widened tip  86  engages with the intermediate component extensions  87  and prevent the telescopic components from pulling out of the housing component in a completely extended screw position. 
       FIGS. 32-35  illustrate another embodiment of the telescopic screw with a housing component  90  containing a screw tip  91  and hollow center  94  with a recess  95  and extension  165  at the other end. The screw contains a telescopic component  93  with a head  89  at one end and extension  99  at the other end. The screw also contains an intermediate telescopic component  92  with an extension  96  on the outside at one end and recess  101  inside along with an extension  100  at the other end. In a retracted position of the screw as shown in  FIG. 33  the intermediate telescopic component  92  is locked by engaging the extension  96  with the recess  95  and the telescopic component  93  is locked by engaging the extension  99  with the recess  101 .  FIG. 34  shows the screw in a partially extended position with the intermediate telescopic portion  92  in an extended position and the telescopic component  93  in a retracted position. The intermediate component extension  96  and the housing component extension  165  prevent the telescopic components from pulling out of the housing component.  FIG. 35  shows the screw in a completely extended position with extensions  99  and  100  preventing the telescopic component from pulling out from the intermediate component. The screw also contains a central hollow component  98  for a screw driver shaft  97 .  FIG. 32  shows the top view of the screw head  89  with the hollow central portion  98 . As shown in  FIGS. 33-35  the screwdriver can be placed in a completely retracted, partially extended, or completely extended screw positions.  FIG. 36  illustrates the screw driver with a shaft  97  and a head  102 .  FIGS. 37-39  illustrate the screw without the screwdriver in place. 
       FIGS. 40-43  illustrate another embodiment of the screw driver with a housing component  106  containing a screw tip  107 , a hollow component  112  with a recess  111  and extension  117 . The screw also contains a telescopic component  110  and an intermediate component  109 . The telescopic component  110  comprises of a head  104  at one end and extension  114  at the other end. The intermediate component  109  is hollow and comprises of an extension  113  on the outside and recess  115  on the inside and extension  116  at the other end. The telescopic screw head  104  also contains holes  105  with corresponding recesses  108  in the housing component for the screw driver shafts. The screw driver as shown in  FIG. 44  contains several shafts  119  and a head  118  and allows placement of the screw in retracted or extended positions.  FIG. 40  shows the screw in a completely retracted position with locking mechanisms engaged.  FIG. 41  shows the top view of the screw head  104  with holes  105  for the screwdriver shafts.  FIG. 42  illustrates the screw driver in a partially extended position and  FIG. 43  shows the screw in a completely extended position. 
       FIG. 45  illustrates a round cranial plate  120  with holes  121  for regular screws and hole  122  for the telescopic screw. The telescopic screw has a larger diameter to accommodate the telescopic components and provide more structural strength.  FIG. 46  illustrates a round plate  123  with recesses  166  to accommodate irregularities on the skull and bone flap surface. The plate also contains holes  124  for the regular screws and  125  for the telescopic screw.  FIG. 47  illustrates a round cranial plate  126  with holes  128  for regular screws and holes  127  for the telescopic screws.  FIG. 48  illustrates a straight plate  129  with a hole  131  for a regular screw and hole  130  for a telescopic screw.  FIG. 49  illustrates a Y-Shape plate with extension  132  with telescopic screw hole  133  and extensions  134  for regular screw holes  135  and  136 .  FIG. 50  illustrates a X-Shape plate with extensions  137  and  139  with telescopic screw holes  138  and  140  and extensions  141  and  143  for regular screw holes  142  and  144 . Other plate shapes can be rectangular or square. 
       FIGS. 51-53  illustrate the constrained outward and inward movement of the bone flap relative to the skull allowed by the cranial fixation plate and telescopic screws.  FIG. 51  illustrates the cranial fixation plate  147  attached to the bone flap  145  with regular screws  148  at one end and attached to the skull  146  with a telescopic screw  149 .  FIG. 52  illustrates the bone flap  145  pushed outwards by an increase in intracranial pressure with the telescopic screw  149  placed in a partially extended position with intermediate telescopic component  151  and housing component  150 .  FIG. 53  illustrates the telescopic screw  149  placed in a completely extended position allowing further outward movement of the bone flap  145  in response to further increase in intracranial pressure. The telescopic screw  149  is shown in complete extension with telescopic component  152 , intermediate telescopic component  151  and housing component  150 . With normalization of the intracranial pressure the pressure on the bone flap is relieved and the telescopic screws fall back into a retracted position approximating the bone flap to the skull. 
     The constrained decompressive craniectomy methodology described in the current patent application is illustrated in  FIGS. 54-60 .  FIG. 54  illustrates the brain  155 , the dura  154 , and the skull  153 .  FIG. 55  illustrates burr holes  156  and  156  created in the skull.  FIG. 56  illustrates part of the skull (bone flap)  157  and dura removed.  FIG. 57  illustrates the bone flap  157  replaced along with a dural patch graft  158  preferably made of an expandable synthetic collagen matrix.  FIG. 58  illustrates the bone flap  157  pushed outwards relative to the skull  153  by the swollen brain  159  to accommodate the increase in intracranial pressure.  FIG. 59  illustrates the bone flap  157  approximated to the skull  153  by cranial fixation plate  160  with regular screw  162  attached to the bone flap and telescopic screw  161  attached to the skull.  FIG. 60  illustrates the swollen brain  159  compressing against the bone flap  157 . The telescopic screw  161  contains the intermediate telescopic component  163  and telescopic head  164  and is placed in an extended position to allow the outward movement of the bone flap  157  relative to the skull  153 . With resolution of the brain swelling the bone flap moves back inwards and the telescopic screws are placed in a retracted position. In case of severe brain swelling, the bone flap cannot be approximated to the skull until the swelling subsides. Placement of the cranial fixation plate requires the telescopic screw to be placed in an extended position. Alternatively, the telescopic screw housing component can be placed into the skull and the telescopic head can be placed after the plate as shown in  FIGS. 61-68 .  FIGS. 61-65  illustrate one embodiment of the telescopic screw. The telescopic component as shown in  FIG. 61  comprises of a head  166  with a recess  167  for the screw driver, extensions  170  and  172  with a proximal wider portion  168  on the outside and recesses  169  on the inside with distal extensions  171 . As shown in  FIG. 62  the extensions  170  and  172  can be compressed together manually  173  and  174  or with an instrument. The recesses  169  allow the extensions  170  and  172  to be compressed together thereby enabling the telescopic component to be placed after the housing component is implanted as shown in  FIG. 63 . The housing component  175  comprises of a screw tip  176 , a hollow portion  178  and extension  177 . As shown in  FIG. 64  the telescopic component  166  is placed in the hollow portion  178  of the housing component  175  with the telescopic extensions  170  and  172  compressed. As shown in  FIG. 65 , the telescopic extensions  170  and  172  resume their normal positions after the compression is relieved. The extensions  171  on the telescopic component and the extension  177  on the housing component prevent the telescopic portion from pulling out from the housing component. The expanded portion  168  of the telescopic extensions engage with the extension  177  when the screw is in a retracted position.  FIGS. 66-68  illustrate another embodiment of the telescopic screw. As shown in  FIG. 66  the screw contains a telescopic component with a head  179 , recess  180 , body  181  and an engaging tip  182 . The screw also contains a housing component with a body  183 , tip  185 , extension  184  and a telescopic slide component with an engaging recess  187  and extension  186 .  FIG. 67  illustrates the telescopic component  181  engaged with the telescopic slide component  187  in a retracted position.  FIG. 68  illustrates the telescopic component  181  in an extended position. The extensions  184  and  186  prevent the telescopic component from pulling out of the housing component. 
     The cranial fixation device can be made of titanium or titanium alloy for MRI imaging compatibility. Other construction materials can include cobalt based alloys, cobalt-chrome alloys, cobalt-chromium-molybdenium, stainless steel alloys, ceramics and polymers. It could also be made of a bio-absorbable material (polyesters, poly amino acids, polyanhydrides, polyorthoesters, polyurethanes, polycarbonates, homopolymers, copolymers of poly lactic acid and poly glycolic acid, copolyesters of e-caprolactone, trimethylene carbonate, and para-dioxanone), or allograft or xenograft bone that is absorbed by the body over time once the bone flap has fused with the skull. Alternatively, it could be made of a radiolucent material like polyetheretherketone (PEEK) or polyaryletherketone (PEAK), high molecular weight polyethylene, carbon fiber, plastic, or a combination of plastic and metal to reduce CT and MRI imaging artifact. The cranial fixation device discussed herein can be of unitary construction and integral or formed of non-integral components attached together. 
     While the invention and methodology described herein along with the illustrations is specific, it is understood that the invention is not limited to the embodiments disclosed. Numerous modifications, rearrangements, and substitutions can be made with those skilled in the art without departing from the spirit of the invention as set forth and defined herein.
The invention provides a method and apparatus for cranial fixation following a craniotomy and treatment for increased intracranial pressure. The cranial fixation device comprises of plates attached to the skull with a telescopic screw. The telescopic screw provides constrained movement of the bone flap relative to the skull to accommodate an increase in the intracranial pressure.