Proprioceptive deficits are comparable before unicondylar and total knee arthroplasties, but greater in the more symptomatic knee of the patient.

The clinical importance of the known proprioceptive deficit in patients with osteoarthritis of the knee is unclear. Attention to the factors that influence proprioception is needed to better understand the role that proprioception plays in the disease process and to assess how these deficits influence clinical outcomes of various treatment options for osteoarthritis. We hypothesized that preoperative proprioception would be poorer in knees with greater symptoms and that knees considered candidates for unicompartmental arthroplasty would have superior proprioception to those in which a total knee arthroplasty was indicated because of the less extensive disease process in the former group. Proprioceptive thresholds were measured in 119 patients with osteoarthritis and no prior knee arthroplasties who were scheduled for unicondylar or total knee arthroplasty. Proprioception examinations consisted of passively flexing and extending each of the bilateral knees in patients independently, from 45 degrees flexion until the blinded patient identified motion. Proprioceptive thresholds for flexion and extension were computed from the angular delays that elapsed before the patient recognized the stimulus. Multiple regression analysis was done to assess the association that these proprioceptive thresholds had with patient factors (age, gender, body mass index, activity level, functional capacity) and knee factors (surgical history, osteoarthritis severity, angular deformity, instability, range of motion). Patient age was the strongest predictor of proprioceptive thresholds, with older patients tending to respond slower to stimulus. Comparison of the right and left knees of each patient showed that proprioception was significantly poorer in the more symptomatic of the two knees. Preoperative thresholds did not differ between knees that received a total knee arthroplasty and those that received a unicondylar arthroplasty.

Total hip arthroplasty in patients 50 years and younger.

Because the young patient with a total hip arthroplasty is presumed to place increased demands on a reconstruction for a longer period than the average patient with a hip replacement, long-term results are expected to be inferior. To determine the efficacy of total hip replacements in this population, the current authors reviewed the long-term results of patients who were 50 years and younger who had cementless total hip arthroplasties at their institution, and reviewed the literature on total hip arthroplasty in younger patients. The results from the study population and the literature were encouraging. At the author's institute, during the past 20 years, 561 hip replacements were done on 488 patients in this age group, using extensively porous-coated cobalt-chromium stems matched with beaded, press-fit acetabular components of cobalt-chrome or titanium. Using the Kaplan-Meier technique, the survival rates for femoral and acetabular components, using any revision as an end point, were 89% at 10-year followup and 60% at 15-year followup. A subset of the authors' patients who were 40 years and younger (256 hips, 223 patients) had slightly inferior results, with 85% 10-year survivorship and 54% 15-year survivorship, using any revision as an end point. A comprehensive literature review also showed that long-term success can be achieved with cemented or cementless total hip arthroplasties in young patients. Because some reconstructions exhibited inferior results in younger patients, the authors recommend that surgeons be much more critical of the components used in these patients and allow long-term data to guide their decisions.

Induction of bone ingrowth from acetabular defects to a porous surface with OP-1.

Reliable ingrowth of bone into porous-coated cementless total hip components can be expected in primary surgery. In the revision scenario, however, bone deficiency frequently is encountered and the remaining bone may have less ingrowth potential. Allograft bone and bone graft substitutes may be successful in healing bone defects, but have virtually no capacity to induce bone growth from the defect into the porous surface. To evaluate the role osteoinductive bone proteins may play in enhancing bone ingrowth, six canines had bilateral total hip arthroplasties with a cementless press-fit porous-coated acetabular component. A defect 8 mm in diameter and 5 mm in depth was created in the superior weightbearing area of each acetabulum. One defect in each animal was filled with recombinant human osteogenic protein-1. Each contralateral defect was filled with allograft bone, left empty (defect healing control), or no defect was created (intact) to serve as a control for ideal conditions for bone ingrowth. The osteogenic protein-treated defects healed more completely than allograft bone-treated or empty defects and achieved a bone density equivalent to the intact acetabulum. Bone ingrowth also occurred to a significantly higher degree in the osteogenic protein group compared with the allograft or empty defects achieving a degree of ingrowth equivalent to the intact acetabulum controls. The osteogenic bone protein was successful in achieving complete defect healing and inducing extensive ingrowth from the defect into the adjacent porous coating.

Analysis of retrieved uncemented porous-coated acetabular components in patients with and without pelvic osteolysis.

Retrieved polyethylene liners and femoral heads from a consecutive series of revision components of one design were examined. All patients had Long-Term Stable Fixation (OsteoTechnology International, Timonium, Md) total hip arthroplasties (THAs) implanted between 1987 and 1992. The retrieved femoral heads and liners from patients with osteolysis were compared to those without osteolysis. Patients with osteolysis had significantly thinner polyethylene (5.1 mm versus 7.4 mm, P<.01 ) and a higher linear wear rate (0.5 mm/y versus 0.3 mm/y, P=.05). The average femoral head surface roughness also was significantly greater in patients with osteolysis (67 nm versus 35 nm, P<.05). Patients with osteolysis had more total volumetric wear, total linear wear, and volumetric wear rate compared to patients without osteolysis. Age, obesity index, time in situ, and cup inclination were not different between the two groups. Excessive polyethylene wear, probably accelerated by surface roughness of the femoral heads, was associated with pelvic osteolysis in these patients.