Instability following total hip arthroplasty (THA) is an unfortunately frequent and serious problem that requires thorough evaluation and preoperative planning before surgical intervention. Prevention through optimal index surgery is of great importance, as the management of an unstable THA is challenging even for an experienced joints surgeon. However, even after well-planned surgery, a significant incidence of recurrent instability still exists. Moreover leg-length discrepancy (LLD) after THA can pose a substantial problem for the orthopaedic surgeon. Such discrepancy has been associated with complications including nerve palsy, low back pain, and abnormal gait. Consequently we may use a big femoral head or increase femoral offset (FO) in unstable THA for avoiding LLD. However we do not know the relationship between FO and STT. The objective of this study is to assess
Abstract. Objectives.
Dual mobility (DM) bearing implants reduce the incidence of dislocation following total hip arthroplasty (THA) and as such they are used for the treatment of
The renewed interest in the clinically proven low wear of the metal-on-metal bearing combined with the capacity of inserting a thin walled cementless acetabular component has fostered the reintroduction of hip resurfacing. As in other forms of conservative hip surgery, i.e. pelvic osteotomies and impingement surgery, patient selection will help minimize complications and the need for early reoperation. Patient Selection and Hip Resurfacing. Although hip resurfacing was initially plagued with high failure rates, the introduction of metal on metal bearings as well as hybrid fixation has shown excellent survivorships of 97 to 99% at 4 to 5 years follow-up. However, it is important to critically look at the initial published results. In all of these series there was some form of patient selection. For example, in the Daniel and associates publications, only patients with osteoarthritis with an age less than 55 were included with 79% of patients being male. Treacy and associates stated that: “the operation was offered to men under the age of 65 years and women under the age of 60 years, with normal bone stock judged by plain radiographs and an expectation that they would return to an active lifestyle, including some sports”. However in the materials and methods, although the mean age is 52 years, the range is from 17 to 76 years including some patients with rheumatoid arthritis as well as osteonecrosis. Obviously, some form of patient selection is needed; but how one integrates them is where the Surface Arthroplasty Risk Index (SARI) is useful. With a maximum score of 6, points are assigned accordingly: femoral head cyst >1cm: 2 points; patient weight <82kg: 2 points; previous hip surgery: 1 point; UCLA Activity level >6: 1 point. A SARI score >3 represented a 4 fold increase risk in early failure or adverse radiological changes and with a survivorship of 89% at four years. The SARI index also proved to be relevant in assessing the outcome of the all cemented McMinn resurfacing implant (Corin¯, Circentester, England) at a mean follow-up of 8.7 years. Hips which had failed or with evidence of radiographic failure on the femoral side had a significantly higher SARI score than the remaining hips, 3.9 versus 1.9. Finally, one must consider the underlying diagnosis when evaluating a patient for hip resurfacing. In cases of dysplasia, acetabular deficiencies combined with the inability of inserting screws through the acetabular component may make initial implant stability unpredictable. This deformity in combination with a significant leg length discrepancy or valgus femoral neck could compromise the functional results of surface arthroplasty, and in those situations a stem type total hip replacement may provide a superior functional outcome. In respect to other diagnoses (osteonecrosis, inflammatory arthritis), initial analyses have not demonstrated any particular diagnostic group at greater risk of earlier failure. The only reservation we have is in patients with compromised renal function since metal ions generated from the metal-on-metal bearing are excreted through the urine and the lack of clearance of these ions may lead to excessive levels in the blood. Surgical Technique. Because resurfacing has not been within the training curriculum of orthopaedic surgeons for the last 2 decades, there will most likely be a learning curve in the integration of this implant within clinical practice. This data was confirmed for hip resurfacing when looking at the Canadian Academic Experience where in the first 50 cases of five arthroplasty surgeons only a 3.2% failure rate was noted of which 1.6% were due to neck fracture. Femoral neck fracture can occur because of significant varus positioning as well as osteonecrosis of the femoral head due to either disruption of the blood supply or over cement penetration. Finally, abnormal wear patterns leading to severe soft tissue reactions are being increasingly recognized and are related to either impingement or vertically placed acetabular components. Although impingement has long been recognized after total hip arthroplasty to limit range of motion and in extreme cases to
