Range of motion after stemmed total hip arthroplasty and hip resurfacing: a clinical study.
Abstract: Range of motion after total hip arthroplasty is becoming an important topic as today's patients present at a younger age and are more active. An effective study design to carry out comparisons of clinical performance between two implants should eliminate patient-related extraneous variables (e.g., age, gender, activity level, among others). The aim of the present study was to compare the range of motion results achieved postoperatively between metal-on-metal hip resurfacing (HR) and conventional total hip arthroplasty (THA) in a cohort of bilateral patients implanted with both designs. Thirty-five patients who had undergone bilateral surgery with one hip receiving an HR device and the contralateral hip receiving a THA were retrospectively selected. Sixty-nine percent of the patients were male, and at the time of implantation of the resurfacing device the mean age of the patients was 53 years. The mean follow-up time was 88 months for the hips treated with HR and 96 months for the hips that received a THA. We found no difference in any of the range of motion measurements between HR and THA even after separating the cohort into two groups based on the femoral head size of the THA (femoral heads under 40 mm and femoral heads greater or equal to 40 mm). Our investigation showed that, for most patients, prosthetic design is unlikely to be a limiting factor of range of motion after surgery provided that the positioning of the acetabular component is adequate.
Article Type: Clinical report
Subject: Clinical trials
Implants, Artificial
Medical research
Medicine, Experimental
Authors: Duff, Michel J. Le
Wisk, Lauren E.
Amstutz, Harlan C.
Pub Date: 04/01/2009
Publication: Name: Bulletin of the NYU Hospital for Joint Diseases Publisher: J. Michael Ryan Publishing Co. Audience: Academic Format: Magazine/Journal Subject: Health Copyright: COPYRIGHT 2009 J. Michael Ryan Publishing Co. ISSN: 1936-9719
Issue: Date: April, 2009 Source Volume: 67 Source Issue: 2
Product: Product Code: 8000200 Medical Research; 9105220 Health Research Programs; 8000240 Epilepsy & Muscle Disease R&D NAICS Code: 54171 Research and Development in the Physical, Engineering, and Life Sciences; 92312 Administration of Public Health Programs SIC Code: 3842 Surgical appliances and supplies
Accession Number: 247449433
Full Text: The revival of hip resurfacing (HR) has been attributed to technological advances in the manufacturing of metal-on-metal bearings. (1) However, the recent shift in patient expectations after hip arthroplasty, with a large emphasis on returning to recreational activities, (2) and the lowering of what is considered an acceptable age for total hip arthroplasty (THA), have driven the need for bone-conserving prosthetic solutions for patients with end-stage osteoarthritis. (3-9) With this younger and more active patient population seeking a return to high activity levels, including sporting activities, (10,11) the effect of prosthetic design on the postoperative range of motion has become an important topic that is regularly brought up by the patients themselves during initial consultations.

So far, most investigations focusing on a comparison of range of motion between conventional THA and HR have been in vitro studies (using computer modeling or a three-dimensional compass) measuring the maximum potential range of motion solely based on impingement of the prosthetic components and the surrounding bony structures.

These various studies concluded that the limiting factor for range of motion is the ratio of the femoral head diameter to the femoral neck diameter, with the advantage going to the THA design when a femoral head of large diameter has been used. (12,13) However, the range of motion at the hip can be determined by other factors in addition to the structure of the bone surrounding the joint, including musculotendinous and ligamentous structures. A clinical study is needed to answer the question of the effect of implant design on the effective postoperative range of motion, taking into account the entire physiology of the hip.

The main problem with previous studies comparing resurfacing with THA has been the differences in patient populations, as surgeons tend to select younger and more active patients for HR. (14) Short of an extensive randomized study, the large variability in range of motion results between patients raises doubts about the possibility of any valid comparisons between independent groups. A study using the same patients as both study group and control group would seem to be an ideal design to control for all the patient-related variables, including baseline flexibility and other functional limitations.

The aim of the present study was to compare the range of motion achieved postoperatively between metal-on-metal resurfacing and conventional THA in a group of patients treated bilaterally with both prosthetic designs.

Materials and Methods

From the senior investigator's (HCA) database, we retrospectively identified 47 patients, who had undergone bilateral hip replacements and currently had a metal-on-metal resurfacing device (Conserve[R] Plus, Wright Medical Technology, Arlington, Tennessee) on one side and a stemmed THA on the contralateral side. From this initial group, 12 patients were excluded because we were unable to provide a range of motion measurement performed by the senior investigator at the time of writing (most of these patients lived outside of California, sometimes in remote locations), leaving the data from 35 patients available for review. All 35 resurfacing surgeries were primary surgeries, while 14 of the contralateral THA were revision surgeries, including 12 conversions to THA from a previous resurfacing device. For 18 patients, the THA was performed first, for 13 patients the HR was performed first, and for four patients, both surgeries were performed under a single anesthesia. All devices were functioning well at last follow-up, with no revisions pending.



Twenty-four patients were male (69%) and 11 were female (31%). At the time of implantation of the resurfacing device, the mean age of the patients was 53 years (range, 36 to 74 years). The diagnoses of the patients included osteoarthritis (24 patients, 68.6%), developmental dysplasia of the hip (6 patients, 17.1%), osteonecrosis (3 patients, 8.6%), epiphyseal dysplasia (1 patient, 2.9%), and ankylosing spondylitis (1 patient, 2.9%). The follow-up visits included patient evaluations with the UCLA (University of California at Los Angeles) hip scoring system, (15) range of motion measurement [all performed by the same observer (HCA)], (16) and radiographic data collection with low anteroposterior and cross-table lateral views. (17) The radiographic review specifically focused on identifying the hips with heterotopic ossification (a possible impairment of range of motion) using the Brooker grading system. (18) We also tracked the hips with radiographic impingement signs (on the resurfacing side) and measured the acetabular component abduction angle.

The mean femoral head diameter for the hips that received a resurfacing device was 47 mm (range, 38 to 52 mm), and for the hips that received a THA, the diameter was 36 mm (range, 28 to 50 mm). This difference was significant (p = 0.0001). For this reason, we chose to present the comparative results between HR and THA, representing not only the whole cohort but also separate subgroups based on the femoral head diameter of the THA. Group 1 (n = 22) was defined by THA with femoral heads smaller than 40 mm (Fig. 1) and group 2 (n = 13) by THA with femoral heads 40 mm or larger (Fig. 2).

Two-sample equal variance t-tests were used to assess the significance of differences between HR and THA, because the analysis compares two sets of hips, not one group of patients. The alpha level was set at p = 0.05.


The mean follow-up of the hips with HR was 88 months (range 16 to 145 months) and 96 months (range, 10 to 254 months) for the hips reconstructed with THA. The mean time between surgeries was 38 months (range, 0 to 128 months).

The mean UCLA pain scores recorded at the last follow-up for each hip were 9 (range, 7 to 10) for the HR side and 9 (range, 4 to 10) for the THA side. This difference was not significant (p = 0.6100).

The postoperative range of motion measurements comparing HR with THA for the entire cohort is summarized in Table 1. None of the differences between the two prosthetic designs reached the significance level. No significant differences were noted between designs in group 1 (small THA femoral heads) or group 2 (large THA femoral heads). These results are displayed in Tables 2 and 3.

We also compared range of motion between HR and THA within the group of patients whose THA was a revision surgery (n = 14). We did not find any significant differences between HR and THA within this group of patients, nor were there any differences between the group of patients who had undergone bilateral primary arthroplasties (n = 21).

On the HR side, seven hips showed heterotopic ossification (HO): six were Brooker grade I and one was Brooker grade III. On the THA side, nine hips showed heterotopic ossification: seven were Brooker grade I and two were Brooker grade II. There was no difference between designs in incidence of HO (p = 0.6171), and the patient with Brooker grade III HO on the HR side had a lower abduction-adduction arc on the resurfacing side (65[degrees] vs 80[degrees] for the THA side), as well as a lower rotation arc (55[degrees] vs 75[degrees] for the THA side), while the flexion arc measurements were identical between the two hips.

Acetabular cup abduction angles were comparable between the two designs, with a mean of 46[degrees] (range, 28[degrees] to 61[degrees]) for HR and 44[degrees] (range, 27[degrees] to 68[degrees]) for THA (p = 0.2326). Two patients (5.7%) had radiographic signs of neck-cup impingement on the superior aspect of the femoral neck on the resurfacing side (Fig. 1). Both patients are asymptomatic. Their abduction measurements on the resurfacing side are similar or greater than those measured on the THA side. Both have acetabular component abduction angles less than 40[degrees] on the HR side.


With the rising popularity of HR, there has been a recent growing concern about the ability to restore range of motion after hip reconstruction with this design because of the reduced head to neck diameter ratio compared to modern THA designs with large femoral heads. The main value of the present study resides in its design, which eliminates a large number of extraneous variables, including patient activity and attitude toward the type of implant received, both of which usually affect the validity of comparisons between resurfacing and THR.

To our knowledge, this is the first time such a study design has been used in a comparison between HR and THA. The disparity of stemmed implants and femoral head sizes used in this study may constitute a limitation, as well as the fact that 14 of the THAs (40%) were implanted as revision surgeries. However, our results show that there is no difference in range of motion achieved postoperatively between HR and THA. Further, these results are still verified after stratification by femoral head size or surgery type (primary vs revision) on the THA side. These results are in contrast with those of in vitro studies (12,13) and indicate that the head-neck ratio is generally not the main limiting factor of range of motion at the hip joint after surgery. In addition, the mean range of motion measurements obtained in this study correlated closely with the values recorded by previous investigators in non-diseased subjects, who had not undergone any surgery. (19-21) This is a further indication that range of motion, in time, returns to normal after hip replacement, independent from the type of implant design.

In our experience, the range of motion in both normal and replaced hips is mainly dependent on the inherent flexibility of the individual patient (22); for example, patients who have developmental dysplasia of the hip almost universally are very flexible (Fig. 1). Also, the range of motion values reported in the present study matched or exceeded those measured in a previous study of 73 resurfaced hips. (22) This result indicates that our relatively small sample was still representative of the population of patients seeking resurfacing as a prosthetic solution for primary or secondary osteoarthritis.

The possibility of impingement of the femoral neck with the acetabular component certainly exists with HR, as reported by Lavigne and colleagues, (23) and seen in two patients from this series, but does not represent the vast majority of patients receiving a resurfacing device. For a patient with a normal neck geometry, to reach impingement typically requires either exceptional flexibility or malpositioning of the acetabular component, in particular a cup abduction angle too low or a lack of cup anteversion. (24)

The combination of in vitro and clinical study results on range of motion after resurfacing should be viewed as complementary rather than antagonistic. In our view, the theoretical limitations yielded by the bone and implant only models do suggest a reduced margin of error for the surgeon in reaching optimal component positioning in order to avoid impingement with resurfacing compared to THA. Appropriate training of the surgeons willing to perform resurfacing and the use of an effective instrumentation for component alignment should be sufficient to provide every patient with an effective joint reconstruction, regardless of the type of device used. However, it is also important for the surgeon to preoperatively assess the patient's desires for postoperative range of motion, which may enable them to participate in varying activities, including sports, ballet, etc., so that the component orientation can be optimized at surgery.


Funding for this study was provided by St. Vincent Medical Center, Los Angeles, and Wright Medical Technology.

Disclosure Statement

Harlan C. Amstutz, M.D., is a consultant for Wright Medical Technology (Arlington, TN). None of the other authors have a financial or proprietary interest in the subject matter or materials discussed, including, but not limited to, employment, consultancies, stock ownership, honoraria, and paid expert testimony.


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Michel J. Le Duff, M.A., Lauren E. Wisk, B.S., and Harlan C. Amstutz, M.D.

Michel J. Le Duff, M.A., Lauren E. Wisk, B.S., and Harlan C. Amstutz, M.D., are from the Joint Replacement Institute, St. Vincent Medical Center, Los Angeles, California.

Correspondence: Harlan C. Amstutz, M.D., Medical Director, Joint Replacement Institute, Suite 400, The S. Mark Taper Building, 2200 West Third Street, Los Angeles, California 90057; harlanamstutz@ dochs.org.
Table 1 Comparative Postoperative Range of Motion Measurements Between
Designs for the Whole Cohort (N = 35)

ROM measurement
([degrees])                  Resurfacing        Total Hip      P-Value

Flexion                    123 (90 to 140)   121 (70 to 140)   0.5930
Flexion contracture          2 (0 to 25)       3 (0 to 20)     0.4503
Flexion arc                121 (80 to 140)   119 (70 to 140)   0.4322
Abduction (in extension)    43 (25 to 50)     43 (30 to 55)    0.6403
Adduction (in extension)    28 (20 to 40)     28 (20 to 40)    0.7907
Abd-Add arc                 71 (45 to 85)     70 (50 to 95)    0.6477
Internal rotation (in       40 (10 to 70)     37 (0 to 65)     0.3595
External rotation (in       35 (15 to 60)     36 (5 to 55)     0.9596
Rotation arc               75 (30 to 115)    72 (30 to 110)    0.5420

Table 2 Comparative Postoperative Range of Motion Measurements Between
Designs for Group 1 (Femoral Head Size Under 40 mm for the THA Side;
N = 22)

ROM measurement
([degrees])                  Resurfacing         Total Hip      P-Value

Flexion                    124 (100 to 140)   121 (70 to 140)   0.3680
Flexion contracture          1 (0 to 10)        2 (0 to 15)     0.2373
Flexion Arc                123 (100 to 140)   118 (70 to 140)   0.2072
Abduction (in extension)    43 (25 to 50)      41 (30 to 50)    0.2468
Adduction (in extension)    27 (20 to 40)      25 (20 to 40)    0.3774
Abd-Add arc                 69 (60 to 80)      66 (50 to 85)    0.1349
Internal rotation (in       41 (15 to 70)      33 (0 to 60)     0.1090
External rotation (in       35 (15 to 60)      35 (15 to 55)    0.9030
Rotation arc                74 (40 to 115)    68 (30 to 100)    0.2218

Table 3 Comparative Postoperative Range of Motion Measurements Between
Designs for Group 2 (Femoral Head Size Greater or Equal to 40 mm for
the THA Side; N = 13)

ROM measurement
([degrees])                  Resurfacing        Total Hip      P-Value

Flexion                    121 (90 to 140)   123 (90 to 140)   0.7803
Flexion contracture          4 (0 to 25)       4 (0 to 20)     0.8981
Flexion arc                118 (80 to 140)   119 (90 to 140)   0.8621
Abduction (in extension)    45 (25 to 50)     46 (30 to 55)    0.5643
Adduction (in extension)    30 (20 to 40)     32 (20 to 40)    0.5677
Abd-Add arc                 75 (45 to 85)     78 (50 to 95)    0.5052
Internal rotation (in       39 (10 to 65)     43 (25 to 65)    0.4452
External rotation (in       37 (20 to 45)     37 (5 to 55)     0.9308
Rotation arc               76 (30 to 110)    80 (35 to 110)    0.6194
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