Effect of increasing implant height on lumbar spine kinematics and foraminal size using the ProDisc-L prosthesis.

STUDY DESIGN: A biomechanical study using human lumbar spines. OBJECTIVE: To test the hypotheses that with increasing implant height (1) the range of motion (ROM) of the implanted segment will decrease, (2) the segmental lordosis will increase, and (3) the size of the neural foramens will increase. SUMMARY OF BACKGROUND DATA: Little is known about the effects of the implant height on the segmental motion and foraminal size at the implanted level. METHODS: Seven human lumbar spines (age, 54.4+/-11.4 years; L1-sacrum) were tested intact, and after discectomy at L4-L5 and sequential insertion of ProDisc-L implants (Synthes Spine, Paoli, PA) of increasing heights (10, 12, and 14 mm). The specimens were tested in flexion (8 Nm) and extension (-6 Nm) with a 400 N follower preload as well as in lateral bending (+/-6 Nm) and axial rotation (+/-5 Nm) without preload. Three-dimensional motions were measured at L4-L5. Foraminal sizes at L4-L5 were measured in the specimen's neutral posture under a 400 N preload for the intact spine and after each implantation using finely graded cylindrical probes. Segmental lordosis was measured in the specimen's neutral posture under a 400 N preload by analyzing digital fluoroscopic images. Effects of implant height on the kinematics, foraminal size, and segmental lordosis were assessed using paired comparisons with Bonferroni correction. RESULTS: Increasing implant height from 10 mm to 14 mm caused a significant decrease (P<0.05) in segmental ROM by up to 37%+/-21% in flexion/extension, 33%+/-18% in lateral bending, and 29%+/-28% in axial rotation. Increasing implant height also produced a significant increase in segmental lordosis (P<0.05): from 9.7 degrees+/-2.9 degrees at 10 mm, to 16.1 degrees+/-5.1 degrees at 14 mm. The increase in foraminal size, while significant, was only 4.6%+/-3.2% when comparing 10 mm to 14 mm implants. CONCLUSION: These results suggest that a smaller implant height should be selected to optimize the ROM of the implanted segment and maintain sagittal balance.

Reconstruction of the hypoplastic thumb.

Thumb hypoplasia is characterized by diminished thumb size, metacarpal adduction, metacarpophalangeal joint instability, thenar muscle hypoplasia or aplasia, extrinsic tendon dysplasia, and in the most severe cases, carpometacarpal joint instability or thumb aplasia. Severe thumb hypoplasia and aplasia are best treated by thumb ablation and pollicization of the index finger. Less severe thumb hypoplasia can be reconstructed by a combination of soft tissue release, first web space local flap coverage, metacarpophalangeal joint collateral ligament and capsule reconstruction, extrinsic tendon tenolysis, and muscle or tendon transfers.

Cementless acetabular fixation at fifteen years. A comparison with the same surgeon's results following acetabular fixation with cement.

BACKGROUND: Loosening of the acetabular component is the major long-term problem associated with total hip arthroplasty with cement. The purpose of the present study was to evaluate the minimum thirteen-year results associated with cementless acetabular components that had been inserted by a single surgeon and to compare them with the results associated with cemented acetabular components that had been inserted by the same surgeon. METHODS: One hundred and twenty consecutive, nonselected primary total hip replacements were performed in 108 patients with use of a Harris-Galante-I cementless acetabular component and a cemented femoral component with a 28-mm head. The patients were evaluated clinically with use of a standard terminology questionnaire, and they were evaluated radiographically for loosening, component migration, wear, and osteolysis. The rates of revision for aseptic loosening and radiographic evidence of loosening for this cohort were compared with the rates for four previously reviewed consecutive series of hips in which the acetabular component had been inserted with cement. All patients were managed by the same surgeon, were followed for thirteen to fifteen years, and were evaluated with use of the same two criteria (revision and loosening) as the end points for Kaplan-Meier analysis. RESULTS: Sixty-six patients (seventy-two hips) were living and forty-two patients (forty-eight hips) had died after thirteen to fifteen years of follow-up. No acetabular component had been revised because of aseptic loosening, and no acetabular component had migrated. With revision of the acetabular component for any reason as the end point, the survival rate was 81% +/- 8% at fifteen years. With revision of the acetabular component for clinical failure (osteolysis, wear, loosening, or dislocation) as the end point, the survival rate was 94% +/- 8% at fifteen years. Among the seventy hips with at least thirteen years of radiographic follow-up, five had pelvic osteolysis and three had had revision of a well-fixed acetabular component because of pelvic osteolysis secondary to polyethylene wear. The mean linear wear rate was 0.15 mm/yr (0.12 mm/yr when one outlier was excluded). CONCLUSIONS: In terms of fixation, Harris-Galante-I cementless acetabular components performed better than did cemented 22-mm-inner-diameter Charnley acetabular components as well as 28-mm-inner-diameter all-polyethylene and metal-backed acetabular components that had been inserted by the same surgeon. However, the rate of wear was greater in association with the Harris-Galante-I cementless components than it was in association with the Charnley cemented all-polyethylene components.