A comparison of standard and high-flexion knees: are we getting what we expected?

Some patients have been less than satisfied with flexion after total knee arthroplasty (TKA). As early designs provided limited flexion, companies have developed high-flexion designs. We conducted a study to compare flexion between 2 standard and 3 high-flexion designs and to compare clinical and radiographic postoperative flexion. Clinical and radiographic measurements were obtained by 3 independent orthopedists. Clinical flexion, with the patient maximally bending his or her knee as far as possible, was measured with a goniometer, recorded, and compared with measurements from lateral radiographs of the knee in the same position. A total of 144 knees (108 patients) were included in the study. Mean preoperative flexion was 110° for both groups, and mean postoperative flexion was 111° clinically and 109° radiographically for the standard designs, and 114° clinically and 117° radiographically for the high-flexion designs (P<.05). The groups had similar preoperative and postoperative Knee Society knee and function scores. Measurements obtained by the 3 independent examiners were highly correlated. Compared with the standard designs, the highflexion designs demonstrated statistically significantly more flexion, though the clinical increase in flexion was relatively small (3º).

Measured flexion following total knee arthroplasty.

Postoperative flexion is an important factor in the outcome of total knee arthroplasty. Although normal activities of daily living require a minimum of 105° to 110° of flexion, patients from non-Western cultures often engage in activities such as kneeling and squatting that require higher flexion. The desire to achieve greater flexion serves as the driving force for prosthetic modifications, including high-flexion designs. Techniques used to measure knee flexion and knee position during measurement are not often described or are different depending on the examiner. The purpose of this study was to compare active (self) and passive (assisted) flexion after successful total knee arthroplasty for 5 prostheses (2 standard and 3 high-flexion) using clinical (goniometer) and radiographic (true lateral radiograph) measurement techniques by different independent examiners.At a mean follow-up of 2.7 years (range, 1-5.6 years), a total of 108 patients (144 total knee arthroplasties) had completed the study. Mean postoperative active flexion was 111° clinically and 109° radiographically for the standard designs and 114° clinically and 117° radiographically for the high-flexion designs. Adding passive flexion increased flexion to 115° clinically and 117° radiographically for the standard designs and 119° clinically and 124° radiographically for the high-flexion designs. Flexion differences between the 2 measurement techniques (active vs passive and clinically vs radiographically) were statistically significant (P<.05). These findings demonstrate the importance of describing how flexion is measured in studies and understanding how the method of measurement can affect the findings.

Cementless femoral fixation in total hip arthroplasty.

Cementless femoral fixation by means of bone ingrowth has been successful in total hip arthroplasty in patients with sufficient bone quality. Consistent bone ingrowth and resultant long-term success involve many factors, including surgical technique, initial mechanical stability achieved at time of implantation, stem design and material, and implant surface. One potential method for achieving faster, more consistent initial bone ingrowth is use of the osteoconductive ceramic hydroxyapatite. In addition, more stable initial fixation most likely improves long-term outcome. In this article, we review the criteria for successful cementless femoral fixation and the long-term results reported in the literature.

Surface roughness of femoral head prostheses after dislocation.

The effects of damaged femoral heads on long-term wear in total hip arthroplasties are not well known. In the study reported here, we compared the surface roughness of dislocated femoral heads, retrieved at time of revision, with that of heads revised for reasons other than dislocation. The dislocated heads, including 6 cobalt-chrome (Co-Cr), 2 oxidized zirconium, and 2 alumina (ceramic) heads, were compared with nondislocated Co-Cr and ceramic heads. Scratch marks on the dislocated Co-Cr and alumina heads were considerably smaller and shallow than those on the dislocated oxidized zirconium heads. Mean surface roughness of the dislocated heads was 368 nm (Co-Cr), 376 nm (alumina), and 2137 nm (oxidized zirconium). On the contrary, the mean surface roughness for nondislocated Co-Cr and alumina heads was 307.44 nm (outlier excluded) and 138.8 nm, respectively. Our data suggest that increased surface damage and roughness can occur after dislocation.

Incidence of 'squeaking' after ceramic-on-ceramic total hip arthroplasty.

UNLABELLED: The incidence of hip "squeak" associated with ceramic-on-ceramic bearings has been variably reported, ranging from 0.7% to 20.9%. We determined the patients' perception of squeaking in 306 patients (336 hips) in whom ceramic-on-ceramic total hip arthroplasties (THAs) were performed between 1997 and 2005. A questionnaire regarding hip noise was obtained by telephone. With a minimum followup of 2 years (mean, 3.9 years; range, 2-10 years), 290 patients (320 or 95% of the THAs) completed the questionnaire. Patients reported hip noise in 55 of the 320 THAs (17%); noise was perceived as squeak in 32 of the 320 (10%). Most squeaking hips (29 of 32) were pain-free and symptom-free. One patient was unhappy with his squeaking hip without pain. Our data suggest a much higher incidence of squeak as perceived by patients than previously reported. LEVEL OF EVIDENCE: Level II, therapeutic study. See Guidelines for Authors for a complete description of levels of evidence.

Early dislocation rate in ceramic-on-ceramic total hip arthroplasty.

Wear debris from metal-on-polyethylene articulation in conventional total hip arthroplasty (THA) may limit THA longevity. Bearing surfaces made of modern ceramic material, with high wear resistance and low fracture risk, have the potential to extend the longevity of THA and make the procedure more suitable for young, active patients. Concerns regarding a ceramic-on-ceramic bearing surface have included potential for a higher incidence of dislocation caused by limited modular neck length and liner options. This prospective study assessed the early dislocation incidence for a ceramic-on-ceramic THA system. Out of the 336 consecutive ceramic-on-ceramic THA performed at our institution over an 8-year (1997-2005) period, 2 (0.6%) sustained dislocation during, and none after, the first postoperative year. Both dislocations were treated with closed reduction. No component fracture or revision for any reason has occurred in this series.

Ceramic-on-ceramic total hip arthroplasty early dislocation rate.

Wear debris from metal-on-polyethylene articulation in conventional total hip arthroplasty can limit the implant's longevity. Modern ceramic material with high wear resistance and low fracture risk has the potential to extend the lifetime of total hip arthroplasty, which makes the procedure potentially more suitable for young, active patients. Concerns with brittle ceramic material include fracture risk, the "squeak" phenomenon, and potentially a higher dislocation rate secondary to limited neck lengths and liner options. We therefore determined the early dislocation rate in modern ceramic-on-ceramic total hip arthroplasty. In 1635 total hip arthroplasties performed over the 9-year period (1996-2005), we observed three anterior and 15 posterior dislocations (1.1%). All were treated successfully, one with a revision and 17 with closed reduction under general anesthesia. Ceramic-on-ceramic total hip arthroplasty can be a good alternative bearing surface with a low dislocation rate.