Wayne O. Southwick

Biomechanical analysis of clinical stability in the cervical spine.

This study was undertaken because there is a dearth of objective information in the literature on the clinical instability of the cervical spine below C2. To our knowledge, it is the first biomechanical investigation designed to analyze clinical stability. We have carried out a quantitative analysis of the behavior of the spine as a function of the systematic destruction of various anatomic elements. Under controlled conditions designed to maintain the biological integrity of the specimens, 17 motion segments from 8 cervical spines were analyzed. The spines were studied with either flexion or extension simulated using physiologic loads. Some of the more important findings are: (1) In sectioning the ligaments, one observes small increments of change followed without warning by sudden, complete disruption of the spine; (2) Removal of the facets alters the motion segment such that in flexion, there is less angular displacement and more horizontal displacement; (3) The anterior ligaments contribute more to stability in extension than the posterior ligaments and in flexion, the converse is true; (4) The adult cervical spine is unstable, or on the brink of instability, when any of the following conditions are present: a) All the anterior or all the posterior elements are destroyed or unable to function. b) More than 3.5 mm horizontal displacement of one vertebra in relation to an adjacent vertebra measured on lateral roentgenograms (resting or flexion-extension). c) More than 11 degrees of rotation difference to that of either adjacent vertebra measured on a resting lateral or flexion-extension roentgenogram. These findings can be aptly applied to clinical situations and when instability as determined by the above criteria is present, surgical fusion or some other method to achieve stability should be seriously considered. Work is continuing on this problem as we do not consider this to be altogether complete or definitive. Hopefully, this initial study will stimulate further scientific and clinical investigations.

Osteotomy through the Lesser Trochanter for Slipped Capital Femoral Epiphysis

The technique for accurate biplane osteotomy at the level of the lesser trochanter for the treatment of slipped capital femoral epiphysis by making reasonably accurate roentgenographic measurements is described and illustrated. Correction of one deformity by producing a reverse deformity at another level may not be esthetically appealing but an osteotomy through the lesser trochanter for slipped capital femoral epiphysis has the following advantages: 1. It does not seem to cause avascular necrosis of the head of the femur; 2. It does not open or directly assault the hip joint; 3. It seems to stimulate early closure of the slipped epiphyseal plate; 4. It does not prevent further corrective surgery at a second stage if need be; 5. If performed accurately it can be expected to restore hip function in almost every patient. Fifty-five patients have been treated by this method and avascular necrosis has not occurred. The results in twenty-six patients followed five years or more are reported in detail. Patients who have the complication of joint-space narrowing (not avascular necrosis) with joint stiffness should be given adequate time and rest, probably three years or more, to allow regeneration of the joint space to occur before consideration is given to reconstructive procedures. A possible mechanism for this narrowing and for the later restoration of the space is discussed.

Acute prolapsed lumbar intervertebral disc. An epidemiologic study with special reference to driving automobiles and cigarette smoking.

An epidemiologic case-control study to identify risk factors for acute prolapsed lumbar intervertebral disc was undertaken in Connecticut during 1979-1981. This paper focuses on nonoccupational factors of possible etiologic significance. Persons in their 30s were affected most frequently. Among surgical cases, the ratio of men to women was 1.5 to 1, while among probable and possible cases not undergoing surgery, the male to female ratio was about 1 to 1. Cigarette smoking in the past year was associated with an increased risk for prolapsed disc. The greater the number of hours spent in a motor vehicle, the higher the risk. Use of Swedish and Japanese cars was associated with a lower-than-average risk, while use of other cars was associated with a higher-than-average risk. For each type of car, older cars were associated with higher risks than newer cars. Variables that did not affect the risk for prolapsed lumbar disc in this study included height, weight, number of pregnancies, number of children, frequency of wearing shoes with high heels, smoking cigars or pipes, and participation in baseball or softball, golf, bowling, swimming, diving from a board, tennis, bicycling or jogging.

Relief of pain by anterior cervical-spine fusion for spondylosis. A report of sixty-five patients.

An extensive evaluation of the results of anterior spine fusion in sixty-five patients with cervical spondylosis showed that good results with respect to relief of pain were Obtained in 90 per cent. The factors predisposing to more favorable results were: presence of radicular symptoms preoperatively, presence of positive roentgenographic findings at only one vertebral level, presence of myelographic defects which correlated with the levels operated on, and achievement of a solid union without interspace collapse. None of these factors, however, were indispensable to a good result. Those factors which were associated with a bad result were: the presence preoperatively of long tract signs and the preoperative presence of subluxation of a vertebra. Psychological testing (Cornell Index) did not differentiate whether the results would be favorable or unfavorable.

The four biomechanical stages of fracture repair

Based on analysis of the torque-angle curves and roentgenographic findings in fifty-three healing tibial fractures in rabbits tested in torsion to failure, four biomechanical stages of fracture healing were defined, as follows: Stage I--failure through original fracture site, with low stiffness; Stage II--failure through original fracture site, with high stiffness; Stage III--failure partially through original fracture site and partially through intact bone, with high stiffness; and Stage IV--failure entirely through intact bone, with high stiffness. These stages correlated with the progressive increases in the average torque and energy absorption to failure as healing progressed and also with the average times since the original experimental fracture. It is hoped that this system of staging will provide both a standard by which important variables related to ultimate strength of healing fractures can be correlated and an objective way to predict delayed unions and non-unions and to determine the level of activity that is safe for patients with a healing fracture.

Cervical facet fusion for control of instability following laminectomy

Cervical laminectomy may compromise the stability of the spine. Posterolateral facet fusion can be used to stabilize the spine after laminectomy and prevent progressive deformity. The procedure includes passing wires through drill holes in the articular processes and binding two longitudinal struts of bone to the posterior columns of the articular processes. Sixty-three p atients with cervical laminectomy and facet fusion were reviewed, and fifty-two of them were followed for one to seventeen years. The reasons for fusion were to control overt spinal instability and deformity or to eliminate motion which may contribute to spondylosis. Solid fusion occurred in fifty of fifty-two patients at a mean of 6.5 months and provided continuing stability without progressive deformity. Although facet fusion is a complex procedure, it provides secure stabilization, does not interfere with decompression, and permits early mobilization of the patient.

The Incidence and Distribution of Slipped Capital Femoral Epiphysis in Connecticut and Southwestern United States

The incidence and distribution of slipped capital femoral epiphysis in Connecticut and in the Southwestern part of the United States were studied. The annual incidence of diagnosed cases among Connecticut residents was estimated to be 3.41 per 100,000 population under age twenty-five, and in New Mexico, 0.71 per 100,000. The ratio of male to female cases in Connecticut, 2.67, was higher than the ratio of 1.70 among Southwestern cases. Median ages at diagnosis were thirteen for males and eleven for females in both regions. Blacks were at greater risk for slipped epiphysis than whites, the annual incidence rates in Connecticut being 7.79 for black males, 6.68 for black females, 4.74 for white males, and 1.64 for white females. Urban-rural differences were slight. In Connecticut, no significant social class gradient was observed, whereas its the Southwest, cases were likely to be residents of poorer communities than controls.

Comparison of cyclic loading versus constant compression in the treatment of long-bone fractures in rabbits.

UNLABELLED The strengths of healing long-bone fractures treated in two different mechanical environments were compared using a rabbit experimental model. Constant compression was applied to one healing tibial fracture, while the other was subjected to cyclic compression. At six weeks of healing, the group of tibial fractures treated with cyclic loading exhibited significantly higher torque and energy absorption to failure and lower stiffness than their pair-mates treated with constant compression. No statistically significant differences were detected at four or eight weeks of healing, although there was a suggestion that compression-treated bones may be stronger in the earlier phases of healing. CLINICAL RELEVANCE This experiment suggests that the requirements for rapid fracture-healing may vary with the stage of healing; that is, rigid immobilization applied during the initial stages of healing followed by intermittent compression during later stages.

An epidemiological study of acute prolapsed cervical intervertebral disc.

In this epidemiological study of acute prolapsed cervical intervertebral disc, we found that people in the fourth decade of life were affected somewhat more frequently than individuals in other age groups, and men with a prolapsed cervical disc outnumbered women by a ratio of 1.4 to one. Factors that were associated relatively strongly with this diagnosis were frequent lifting of heavy objects on the job that was held around the time of the onset of symptoms, cigarette-smoking, and frequent diving from a board. Positive associations that were of borderline statistical significance or were not statistically significant were found with operating or driving vibrating equipment and time spent in motor vehicles. Variables that did not appear to affect the risk for a prolapsed cervical disc included participation in certain sports other than diving, frequent wearing of shoes with high heels, the number of pregnancies or live births, frequent twisting of the neck on the job, time spent sitting on the job, and smoking cigars or a pipe.

Atlanto-axial fusion for instability.

The problem of how best to treat a patient with instability of the atlanto-axial complex is still somewhat controversial. In this follow-up study of fifty-nine patients, nineteen were treated by a plaster jacket and brace; eleven, by single midline wiring and onlay bone grafts; and thirty, by four circumferential wires around the posterior elements of the axis and atlas with two bone grafts wedged between these elements on each side according to the method described by Brooks and Jenkins. (One patient had both types of fusion.) Although direct comparison of the results of treatment in three groups was not possible because of the many variables that may have influenced the results, the incidence of solid fusion was distinctly higher after the Brooks fusions despite less postoperative immobilization.