Total hip arthroplasty in patients 16 years of age or younger.

PURPOSE: Total hip arthroplasty (THA) is rarely recommended in skeletally immature patients. The goal of the present study was to report our short- to mid-term results of THA in a series of children aged 16 years or younger, including clinical outcomes and post-operative complications, signs of radiographic loosening of the prostheses, and revision rate. METHODS: The 18 children (two male and 16 female patients, 24 hips) underwent cementless THA at a mean age of 14.6 years (11 to 16). Five patients had a bilateral, one-stage surgical procedure. Clinical assessment of these hips used the Merle d'Aubigné et Postel scale modified by Charnley to facilitate assessment of the function of walking. Clinical and radiographic follow-up was conducted at six weeks, six months and then yearly for the first three years. All post-operative complications were recorded. RESULTS: No intra-operative or early post-operative complications occurred. At a mean follow-up of 3.8 years (1 to 8), all patients had greatly improved pain and function scores. All children in the present study improved from severely impaired gait, including four children who were wheelchair-bound, to completely unrestricted gait. All hips demonstrated good alignment with no evidence of wear or radiographic lucencies. No revision of components has been required. One patient had persistent adductor contracture which was addressed with adductor tendon release. CONCLUSIONS: THA is a successful procedure for unsalvageable hip arthritis in children at a mean follow-up of 3.8 years. Long-term follow-up will be needed to determine implant longevity of the components in these children.

Feasibility of osteosynthesis of fractured cadaveric hips following preventive elastomer femoroplasty.

BACKGROUND: In vitro cadaveric studies showed that elastomer femoroplasty prevents displacement of fracture parts after proximal hip fracture allowing for conservative treatment. In the event that secondary displacement does occur, the purpose of this present study was to determine the feasibility of performing osteosynthesis of a fractured hip after preventive treatment with elastomer femoroplasty. METHODS: Ten pairs of human cadaveric femurs were fractured in a simulated fall configuration. From each pair, one femur was randomly selected for elastomer femoroplasty prior to fracture generation and the contralateral femur was used as control. Following hip fracture generation, osteosynthesis was performed in all femurs. The operative time per case, technical difficulties during the procedure, and postoperative energy-to-failure load were recorded. RESULTS: The mean (SD) time to perform osteosynthesis was 20 (6) minutes in the control-group and 19 (5) minutes in the elastomer femoroplasty-group (P=0.69). During osteosynthesis of the fractured hip in the elastomer femoroplasty-group, no difficulties including the need for additional instruments to remove elastomer from the proximal femur were recorded. Postoperative energy-to-failure load was similar in the control-group and the elastomer femoroplasty-group. CONCLUSION: Fixation with routine osteosynthesis of displaced cadaveric hip fractures is not hindered by the presence of previously injected elastomer.

In-vivo time-dependent articular cartilage contact behavior of the tibiofemoral joint.

OBJECTIVE: The purpose of this study was to investigate the in-vivo time-dependent contact behavior of tibiofemoral cartilage of human subjects during the first 300 s after applying a constant full body weight loading and determine whether there are differences in cartilage contact responses between the medial and lateral compartments. DESIGN: Six healthy knees were investigated in this study. Each knee joint was subjected to full body weight loading and the in-vivo positions of the knee were captured by two orthogonal fluoroscopes during the first 300 s after applying the load. Three-dimensional models of the knee were created from MR images and used to reproduce the in-vivo knee positions recorded by the fluoroscopes. The time-dependent contact behavior of the cartilage was represented using the peak cartilage contact deformation and the cartilage contact area as functions of time under the constant full body weight. RESULTS: Both medial and lateral compartments showed a rapid increase in contact deformation and contact area during the first 20s of loading. After 50s of loading, the peak contact deformation values were 10.5+/-0.8% (medial) and 12.6+/-3.4% (lateral), and the contact areas were 223.9+/-14.8 mm(2) (medial) and 123.0+/-22.8 mm(2) (lateral). Thereafter, the peak cartilage contact deformation and contact area remained relatively constant. The respective changing rates of cartilage contact deformation were 1.4+/-0.9%/s (medial) and 3.1+/-2.5%/s (lateral); and of contact areas were 40.6+/-20.8 mm(2)/s (medial) and 24.0+/-11.4 mm(2)/s (lateral), at the first second of loading. Beyond 50 s, both changing rates approached zero. CONCLUSIONS: The peak cartilage contact deformation increased rapidly within the first 20s of loading and remained relatively constant after approximately 50 s of loading. The time-dependent response of cartilage contact behavior under constant full body weight loading was significantly different in the medial and lateral tibiofemoral compartments, with greater peak cartilage contact deformation on the lateral side and greater contact area on the medial side. These data can provide insight into normal in-vivo cartilage function and provide guidelines for the improvement of ex-vivo cartilage experiments and the validation of computational models that simulate human knee joint contact.

In vivo cartilage contact deformation in the healthy human tibiofemoral joint.

OBJECTIVES: In vivo cartilage contact deformation is instrumental for understanding human joint function and degeneration. This study measured the total deformation of contacting articular cartilage in the human tibiofemoral joint during in vivo weight-bearing flexion. METHODS: Eleven healthy knees were magnetic resonance (MR) scanned and imaged with a dual fluoroscopic system while the subject performed a weight-bearing single-leg lunge. The tibia, femur and associated articulating cartilage were constructed from the MR images and combined with the dual fluoroscopic images to determine in vivo cartilage contact deformation from full extension to 120 degrees of flexion. RESULTS: In both compartments, minimum peak compartmental contact deformation occurred at 30 degrees of flexion (24 +/- 6% medial, 17 +/- 7% lateral) and maximum peak compartmental deformation occurred at 120 degrees of flexion (30 +/- 13% medial, 30 +/- 10% lateral) during the weight-bearing flexion from full extension to 120 degrees. Average medial contact areas and peak contact deformations were significantly greater than lateral compartment values (P < 0.05). In addition, cartilage thickness in regions of contact was on average 1.4- and 1.1-times thicker than the average thickness of the tibial and femoral cartilage surfaces, respectively (P < 0.05). CONCLUSIONS: These data may provide base-line knowledge for investigating the effects of various knee injuries on joint contact biomechanics and the aetiology of cartilage degeneration.