John R. Moreland

Wear is a function of use, not time

Polyethylene wear (linear penetration) in 37 hip replacements was assessed from digital images using a validated two-dimensional, edge detection-based computer algorithm. Patient activity was assessed with a pedometer, a step activity monitor and a simple visual analog scale. Joint use was related to wear at the 90% confidence level. Without three recognized outliers, wear was highly correlated to use. The visual analog scale activity rating was significantly related to wear for the 24 hip replacements with standard polyethylene. Univariate regression analysis indicated that male gender, height, weight (which were both highly correlated to male gender) and hip center of rotation were significantly correlated to wear. Multivariate regression analysis indicated that male gender, femoral off-set, and Hylamer® were significantly correlated to wear. Based on the wear and activity data from the 24 hip replacements with standard polyethylene, the average volumetric wear rate per million cycles with a 70 kg patient weight was 30 mm3. This unique in vivo result can be considered a target wear rate for standard polyethylene in hip simulator studies.

Femoral revision hip arthroplasty with uncemented, porous-coated stems.

One hundred seventy-five cementless femoral hip revision surgeries with extensively porous-coated stems and 161 concomitant acetabular revisions done from 1984 to 1991 were retrospectively reviewed. Average age at surgery was 62.4 years. Followup ranged from 2 to 10 years (average, 5 years). One hundred sixty-eight femoral components (96%) remain in place. Two unstable components, 1 stable fibrous component, and 1 bone ingrowth component were painful and required rerevision. Two femoral components were removed as part of resection arthroplasties for repetitive acetabular failure caused by pelvic dissociation. One component was removed for late hematogenous infection. Using the Engh radiographic criteria, femoral stems were judged to have achieved bony ingrowth in 82.8% (n = 174) of the cases. Bony ingrowth occurred more frequently when the canal was filled with the prosthesis and with lesser degrees of bone stock deficiency. Severe stress shielding occurred in 11 (7.6%; n = 144) of the bone in-grown cases and correlated with preoperative osteoporosis and larger diameter prosthesis. Significant thigh pain was less common in the bone ingrown (4.2%; n = 144) than in the stable fibrous group (18.5%; n = 27). Significant thigh pain in bone ingrown stems was more likely to occur with osteoporotic and bone stock-deficient femurs. To date, significant wear and osteolysis have not been observed.

Catastrophic wear of tibial polyethylene inserts.

A number of factors play an important role in the wear-resistance of tibial polyethylene inserts. Among these are manufacturing processes that adversely affect the wear-resistance of polyethylene (such as heat treatments to the articular surface or gamma irradiation used for sterilization), tibiofemoral articular geometry, polyethylene thickness, knee alignment, femoral-component- bearing surface material, modularity of the tibial inserts and tibial trays, and quality of the polyethylene itself. The authors report an unusually high rate of failure by wear of tibial polyethylene inserts from a series of 176 Porous Coated Anatomic (PCA) knees in which there were eight revisions (4.5% of the series) performed for tibial polyethylene wear at an average of 60 months. Nine additional knees (5.1%) had thinning of greater than 30% of the initial polyethylene thickness. Four of the unsuccessful knees revealed areas of osteolysis filled with membranes containing large amounts of particulate polyethylene. In addition to the 176 knees from a series from a Los Angeles university, the cases of five other knees in four patients who came for treatment from outside hospitals with full-thickness wear of the tibial polyethylene are discussed. One of these five knees was a cementless PCA knee that developed massive osteolysis in response to the particulate polyethylene debris.

Cementless femoral revision arthroplasty of the hip: minimum 5 years followup.

Durable fixation of the femoral component to the bone in femoral revision arthroplasty of the hip is the main ingredient to a successful reconstruction. Because of poor durability of cemented fixation in revision, in 1984, one author began to use cementless fixation with extensively porous-coated chrome cobalt stems. The current authors report the durability of that fixation technique in 137 hips (134 patients) followed up 5 to 16 years. With a mean followup of 9.3 years, 10 (7%) of the stems have been removed. Five (4%) were removed for fixation problems and five (4%) were removed for infection. Using the radiographic criteria of Engh et al, 83% of the stems achieved bony ingrowth. No late failure of fixation was observed. Canalfilling prostheses were more likely to have bone ingrowth as were stems placed in femurs with lesser degrees of bone stock deficiency. Significant thigh pain was seen in 7% of bone ingrown stems, 16% of stable fibrous fixated stems, and 75% of unstable stems. Significant thigh pain in bone ingrown stems was observed more commonly in osteoporotic femurs and bone stock deficient femurs. Severe stress shielding correlated with preoperative osteoporosis and larger diameter stems but has not caused failure. Excellent durability of this fixation technique is evident.

Nutritional status and wound healing in lower extremity amputations.

This prospective study examines the importance of nutritional status in 41 consecutive patients with lower extremity amputations proximal to the Symes level. The nutritional status of the patients was assessed by evaluating serum albumin levels and total lymphocyte counts, proven indices of nutritional status. Fifteen of 16 patients with normal nutritional parameters healed their amputations uneventfully, whereas 11 of 25 malnourished patients suffered either local or systemic postoperative complications. The difference in the complication rate between the nourished and malnourished groups is statistically significant (p less than 0.05). Malnutrition adversely affects the prognosis for healing lower extremity amputations, but it seems to be less detrimental to wound healing in the more proximal amputations, where blood flow is superior. Based on these findings, it is recommended that patients being admitted for lower extremity amputation should be screened at the time of admission, and those with laboratory parameters indicative of malnutrition should have elective surgery postponed until their malnourished state is corrected. Patients requiring urgent surgical treatment should probably receive supplemental nourishment in the perioperative period.

Uncemented Total Hip Arthroplasty in Rheumatoid Arthritis Diseases: A Two-to Six-year Follow-up Study

Forty primary uncemented total hip arthroplasties (THAs) were performed in 34 patients with an average age of 41.2 years (range, 21-78 years). Four hips had one component placed with cement: three femoral, one acetabular. Diagnoses included rheumatoid arthritis (30 hips), juvenile rheumatoid arthritis (seven hips), and systemic lupus erythematosus (three hips). The follow-up period averaged 3.7 years (range, two to six years). Thirty-five percent of the patients were using corticosteroids before hip replacement and throughout the follow-up period, whereas 44% of the patients had been using steroids in the past. Additionally, 79% of the patients were taking some form of antiinflammatory medications at follow-up examination. Clinical evaluation based on a ten-point rating scale indicated significant improvements from preoperative to the most recent follow-up examination for pain (from 3.1 to 9.0), walking (4.0-7.3), function (3.5-6.0), and activity (3.0-4.9). None of the hips required revision surgery, and none are pending. There was no evidence of roentgenographic failure; however, 43% of femoral and 12.8% of acetabular components showed some minor radiolucencies with sclerotic lines. None of these involved 100% of the bone-prosthesis interface. Femoral component subsidence occurred in two hips, and acetabular component migration occurred in one hip. Complications included three (8.1%) intraoperative femoral fractures, of which two required internal fixation. One patient had postoperative, culture negative, wound drainage. No deep sepsis occurred. These findings suggest that uncemented THA may be successful in the rheumatoid patient. Pain relief, walking, function, and activity levels are similar to those seen in cemented replacements with this length of follow-up period.(ABSTRACT TRUNCATED AT 250 WORDS)

The window technique for the removal of broken femoral stems in total hip replacement

Removal of broken femoral stems continues to be a difficult technical procedure in hip replacement surgery, despite the development of metal drilling devices and special extractors placed into the drill hole. The window technique for the removal of broken femoral stems is technically easier than the metal drilling technique and does not require sophisticated instrumentation. This technique is also useful as a back-up procedure when metal drilling procedures fail.

Fracture of a unicompartmental knee replacement femoral component

Fracture of the femoral component of a unicompartmental knee replacement occurred ten years after the operation in a 69-year-old man. Fractures of femoral components are unusual and can occur when the metal is thin and weak or where there are areas of stress concentration.

Fracture of a Charnley acetabular component from polyethylene wear.

A 42-year-old man incurred a fracture of the high-density polyethylene socket eight years after a Charnley arthroplasty with a 22 mm head. The excessive wear debris resulted in severe tissue reaction and included resorption of surrounding cancellous bone stock. Polyethylene component wear, occasionally seen in total hip arthroplasties, may be relatively more common in hip replacements that do not fail from loosening.