James B. Carr

1991 Volvo Award in Experimental Studies: Cauda Equina Syndrome: Neurologic Recovery Following Immediate, Early, or Late Decompression

An animal model of cauda equina syndrome was developed. Neurologic recovery was analyzed following immediate, early, and delayed decompression. Five experimental groups, each containing six dogs, were studied. Compression of the cauda equina was performed in all 30 dogs following an L6-7 laminectomy. The cauda equina was constricted by 75% in each group. The first group was constricted and immediately decompressed. The remaining groups were constricted for 1 hour, 6 hours, 24 hours, and 1 week, respectively, before being decompressed. Somatosensory evoked potentials were performed before and after surgery, before and immediately after decompression, and 6 weeks following decompression. Daily neurologic exams using the Tarlov grading scale were performed. At 6 weeks postdecompression, all dogs were killed, and the neural elements analyzed histologically. Following compression, all 30 dogs had significant lower extremity weakness, tail paralysis, and urinary incontinence. All dogs recovered significant motor function 6 weeks following decompression. The dogs with immediate decompression generally recovered neurologic function within 2-5 days. The dogs receiving 1-hour and 6-hour compression recovered within 5-7 days. The dogs receiving 24-hour compression remained paraparetic 5-7 days, with bladder dysfunction for 7-10 days and tail dysfunction persisting for 4 weeks. The dogs with compression for 1 week were paraparetic (Tarlov Grade 2 or 3) and incontinent during the duration of cauda equina compression. They recovered to walking by 1 week and Tarlov Grade 5 with bladder and tail control at the time of euthanasia. Immediately after compression, all five groups demonstrated at least 50% deterioration of the posterior tibial nerve evoked potential amplitudes. Six weeks after decompression, all five groups had a mean amplitude recovery of 20-30%. There were no statistical differences in recovery of somatosensory evoked potentials among the groups. Histologic analysis of the cauda equina in all groups demonstrated scattered wallerian degeneration and axonal regeneration. Areas of poor myelination, fibrosis, and macrophage activity were seen at the level of constriction. There were no significant differences in the histologic neuroanatomy of the five groups. It has been advocated that early decompression of cauda equina syndrome enhances neurologic recovery. This study does not support this premise. Although decompression allowed significant recovery in all 30 dogs, no significant differences were found in somatosensory evoked potentials, neurologic recovery, or histopathology in groups decompressed immediately, at 1 hour, 6 hours, 24 hours, or 1 week.

Mechanism and pathoanatomy of the intraarticular calcaneal fracture

The mechanism and pathoanatomy of the acute intraarticular calcaneal fracture is produced by axial loading. A combination of shear and compression forces produce two characteristic primary fracture lines. Shearing forces produce a fracture dividing the calcaneus into medial and lateral portions. This fracture line typically splits the posterior facet and can extend anteriorly to involve the anterior and cuboid facets. Compression forces divide the calcaneus into anterior and posterior portions. This fracture line can extend medially to involve the middle facet. Loss of calcaneal height and length are readily explained by this mechanism.

Surgical treatment of intra-articular calcaneal fractures: a review of small incision approaches.

This review article covers the use of small incision open reduction and internal fixation for the treatment of the intra-articular calcaneal fracture. The central concept is to match the fracture anatomy with the appropriate surgical approach. Covered first is the mechanism and pathoanatomy, which produces a stereotypical pattern. The major components to address include the posterior facet, superomedial fragment, anterolateral fragment, and tuberosity. The choices of approaches discussed are percutaneous, lateral, medial, and combined. A reduction strategy follows that of the extensile approach, and the goal is total anatomic restoration. Fixation consists of small fragment implants, minifragment implants, and K wires. Specific fracture patterns amenable to selective small incision approaches are described. Detailed surgical strategies are provided. These techniques will be placed in the context of pertinent literature on this subject.

Biomechanical comparison of ankle arthrodesis techniques: crossed screws vs. blade plate.

Many different techniques for ankle arthrodesis have been described. Experience at our institution with crossed screws internal fixation has not met the 90+% union rate reported in the literature. A compression blade plate is one technique for ankle arthrodesis which has not been evaluated biomechanically. A biomechanical study comparing two groups of sawbone ankle fusion constructs fixed with crossed screws and compression blade plates was performed in order to evaluate the stiffness and rigidity of these two arthrodesis techniques. The crossed screws construct demonstrated superior stiffness during dorsiflexion (p < 0.001) and valgus (p < 0.001) loading. The two constructs were found to have equal strength in resisting plantarflexion, varus and torsional loads although there was a trend for greater resistance by the crossed screws construct. These findings lend biomechanical support to the use of crossed screws for tibiotalar arthrodesis.

Comparison of the syndesmotic staple to the transsyndesmotic screw: a biomechanical study.

Background: Controversy still exists about treatment of syndesmotic injuries. This study compared the fixation strengths and biomechanical characteristics of two types of ankle fracture syndesmotic fixation devices: the barbed, round staple and the 4.5-mm cortical screw. Methods: Cadaveric testing was done on 21 fresh-frozen knee disarticulation specimens in biaxial servohydraulic Instron testing equipment. Submaximal torsional loads were applied to specimens in intact and Weber C bimalleolar fracture states. The specimens were then fixed with one of two techniques and again subjected to submaximal torsion and torsion to failure. Biomechanical parameters measured included tibiofibular translation and rotation, maximal torque to failure, and degrees of rotation at failure. Results: Compared to the intact state before testing, the staple held the fibula in a more anatomic position than the screw for mediolateral and anterior displacements (p < 0.01). With submaximal torsional testing, the staple restored 85% of the tibiofibular external rotation and all of the posterior translation values as compared to the intact state. The screw resulted in 203% more tibiofibular medial translation and 115% more external rotation than the intact state. The degree of tibial rotation during submaximal torsional loading was restored to within 15% of intact values but was 21% less with the screw. There was no statistical difference between the screw and staple when tested in load to failure. Tibio-talar rotation at failure was statistically different with the staple construct, allowing more rotation as compared to the screw. Conclusion: The staple restored a more physiologic position of the fibula compared to the syndesmotic screw. Both provided similar performance for the load to failure testing, while the screw reduced tibial rotation more after cyclic loading. There was more tibial rotation before failure for the staple, suggesting a more elastic construct. This study provides biomechanical data to support the clinical use of the syndesmotic staple.

Internal fixation of experimental intraarticular calcaneal fractures: a biomechanical analysis of two fixation methods.

OBJECTIVE To evaluate and compare the mechanical stability of two different fixation techniques on experimentally induced calcaneus fractures. METHODS Thirteen fresh frozen cadaver lower limbs had intraarticular calcaneal fractures produced with an impact loading device. Internal fixation was then performed through lateral and medial approaches using 3.5-mm interfragmentary screws fixed to the posterior facet. Next, either a five-hole 1/3 tubular or five-hole reconstruction plate was placed on the lateral cortex. Radiographs were obtained to confirm reduction. The foot was then cyclically loaded for 500 cycles with a compressive load of 98 N, followed by loading to failure. RESULTS The displacement at the posterior facet fracture line between the loaded and unloaded foot at the 500th cycle was 0.30 +/- 0.08 mm and 0.39 +/- 0.18 mm for the tubular and reconstruction plates, respectively. These displacements were not statistically significant (Students t test p > 0.3). The load and displacement at failure for the tubular plate were 2021 +/- 1050 N and 6.10 +/- 1.75 mm, respectively. Those for the reconstruction plate were 1923 +/- 697 N and 4.57 +/- 1.32 mm (p > 0.09). CONCLUSION This study supports the mechanical viability of using less prominent plates for the fixation of intra-articular calcaneal fractures.

Lumbar spinal stenosis secondary to calcium pyrophosphate crystal deposition (pseudogout)

A 62-year-old man demonstrated symptoms, signs, and radiographic evidence of lumbar spinal stenosis and intraoperative pathologic findings of tophaceous deposition in the ligamentum flavum. Although there have been reports of cervical calcium pyrophosphate dihydrate crystal deposition (CPPD) with neurologic compression, this report appears to be the first case of lumbar spinal stenosis secondary to CPPD. Cervical calcium pyrophosphate dihydrate crystal deposition should be added to the differential diagnosis of spinal stenosis.

A comparison of femoral neck fixation with the reconstruction nail versus cancellous screws in anatomic specimens

Femoral neck fixation techniques were applied to five matched pairs of autopsy specimens to evaluate the fixation of the Russell-Taylor femoral nail in ipsilateral neck and shaft fractures of the femur. Reconstruction nail fixation of the femoral neck was compared with that of three parallel screws. The intact and postfixation femora were subjected to an applied bending moment in 0°, 30°, and 90° of simulated hip flexion. The bending stiffness was determined from the load deformation data for each intact femur and then after the appropriate fixation. The fatigue response of the fixation, presence of osteopenia, degree of fracture reduction, and device alignment showed that the stiffness ratio (fixed to normal) of the nail was greater in most specimens. There was no statistical difference in retained stiffness after cyclic loading between the nail and cancellous screw fixations. The ultimate strength of the nail was 2.5 times the strength of the screw fixation of the femoral neck. Thus, the nail provided biomechanically sound fixation of the femoral neck.

Varus of the talus in the ankle mortise secondary to calcaneus fracture. A case report.

Varus displacement of the talus in the ankle mortise secondary to a calcaneus fracture was observed in a 33-year-old man. Similar to the calcaneus fracture-dislocation, the mechanism involved inferior and medial displacement of the talus into the body of the calcaneus. The patients ankle deformity was not corrected by a lateral ankle ligament reconstruction. Correction required a distraction subtalar bone block fusion. Successful reconstruction of the hindfoot after calcaneus fractures requires a careful analysis of the pathologic lesion. In this unusual case, correction required restoration of lost hindfoot bone structure.

HTLV-I viral-associated myelopathy after blood transfusion in a multiple trauma patient.

This may be the first documented case in the United States and in the orthopedic literature of transfusion-transmitted human T-cell leukemia virus Type I (HTLV-I)-associated myelopathy (HAM). Progressive myelopathy occurred in a 58-year-old white man with serologic and molecular evidence of HTLV-I infection after multiple trauma and subsequent transfusion with multiple units of banked blood products. Symptoms of myelopathy occurred 15 months after the transfusions. Myelopathy from HTLV-I infection simulates a disorder of orthopedic interest. Physicians should be aware of the symptoms of HAM and unexplained myelopathy.