A comparison of total hip resurfacing and total hip arthroplasty: Patients and Outcomes.
Abstract: A comparison of pertinent preoperative and postoperative data relative to total hip resurfacing versus total hip arthroplasty (THA) would assist in evaluating current perceptions in outcome. We compared 50 consecutive metal-metal resurfacing replacements in 50 patients with 44 consecutive conventional total hip arthroplasties in 35 patients, who were implanted during the same time period, by the same surgeon, and followed prospectively for 2 to 4 years. The patients undergoing hip resurfacing were 62% male, 9 years younger, and 3.2 inches taller, with a lower mean body mass index and American Society of Anesthesiologists (ASA) grade than patients undergoing total hip arthroplasty. Preoperatively, patients undergoing resurfacing had a lower Harris hip score (46 vs 52 points), more pain, higher UCLA (University of California at Los Angeles) activity scores (4.2 vs 3.6), and better range of motion. Surgical time for resurfacing was 18% longer, but there was less total blood loss and fewer transfusions. Postoperatively, there was no difference in Harris hip score (97 vs 96). Patients undergoing resurfacing had higher function, Short Form-12 physical activity scores, and UCLA activity scores, but also a higher incidence of slight or mild pain. There were no differences in postoperative range of motion or dislocation (one each). The preoperative characteristics and general health status of the average patient undergoing resurfacing are more favorable than that of the average patient undergoing conventional total hip arthroplasty. Caution should be applied in attributing differences in outcomes directly to the arthroplasty technology.
Subject: Body mass index (Analysis)
Authors: Fowble, Vincent A.
dela Rosa, Mylene A.
Schmalzried, Thomas P.
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
Accession Number: 247449418
Full Text: Metal-metal surface replacement (MMSR) has seen increased utilization around the world.1 This growth is fueled in the orthopaedic community by reports of favorable outcomes in peer-reviewed publications.2-4 Patient interest in hip resurfacing in the United States (U.S.) is partly driven by Internet promotions and patient postings reporting faster recovery and greater functional capacity, including a higher range of motion (ROM) and lower dislocation risk than with traditional total hip arthroplasties (THAs). In fact, there is a paucity of comparisons in the literature of patients and outcomes with current generation MMSRs and THA. The following investigation is a comparative study of patient demographics, preoperative clinical condition, and postoperative outcome across these two procedures. We hypothesize that the functional benefits of MMSR are due, at least in part, to patient-related variables, such as age and general health status.

Materials and Methods

Pertinent pre- and postoperative data of two cohorts receiving either hip resurfacing or conventional hip arthroplasty were identified and evaluated as per the following: 50 consecutive hips in 50 patients who underwent hip resurfacing were compared with 44 consecutive hips in 35 patients who underwent contemporary conventional THA by the same surgeon (TPS), at the same hospital, and during the same time period. All patients who underwent MMSR were selfreferred specifically for MMSR. Patients undergoing hip resurfacing were predominantly male (62% male for MMSR vs 41% male for THA; p = 0.03) and an average of 9 years younger than patients undergoing THA (46 years vs 55 years, respectively; p = 0.0001). Patients undergoing resurfacing were, on average, 3.2 inches taller (p < 0.0001), with lower (p = 0.0009) mean body mass index (BMI) (27.3 kg/m2 vs 31.1 kg/m2). Patients undergoing resurfacing more often (p = 0.001) had unilateral disease (82% vs 48% Charnley A) and lower (p = 0.001) American Society of Anesthesiologists scores,5 indicating less comorbidity and better general health (Table 1). The minimum follow-up was 2 years. Total hip resurfacing implants were considered investigational by the U.S. Food and Drug Administration (FDA). The research protocol and informed consent for this study were approved by the hospital Institutional Review Board and conducted under the auspices of the FDA with an investigational device exemption (IDE).

A hybrid metal-on-metal resurfacing prosthesis (Conserve[R] Plus; Wright Medical Technology, Arlington, Tennessee) was used in the resurfacing procedures. The THA surgeries employed cementless femoral and acetabular components (Summit[R] and Pinnacle[R]; DePuy Orthopaedics,

Inc., Warsaw, Indiana) with either a cross-linked polyethylene bearing (30 hips, 25 patients; Marathon, DePuy Orthopaedics, Inc.) or a metal bearing (14 hips, 10 patients; Ultamet[R], DePuy Orthopaedics, Inc.). All surgeries were performed through a posterolateral approach, with repair of the posterior capsule and external rotators. In general, the dissection to obtain adequate exposure for resurfacing was variably more extensive at all tissue planes than for THA. Perioperative antibiotics, postoperative suction drains, and thromboembolic prophylaxis with a low-molecular-weight heparin were routine in all cases. All resurfacing patients and all male THA patients received indomethacin for the first 7 postoperative days for prophylaxis against heterotopic ossification. All hips followed the same postoperative physical therapy protocols, with activity as tolerated. No patient was advised to restrict his or her postoperative activity.

Two study investigators (VAF and TPS) followed patients prospectively, and clinical outcomes were assessed with the Harris hip score, (6) Short Form-12 (SF-12) questionnaire, (7) and the University of California, Los Angeles (UCLA) activity score. (8)

Differences among and within the two groups were evaluated using the paired Student's t-test or Fisher's exact t-test. Statistical analysis was performed with Stata 5.0 software (Stata, College Station, Texas).

Results

Hip resurfacing procedures had longer average surgical times (the time from completion of anesthetic induction until the patient was returned to a supine position after the procedure): 174 versus 148 minutes (p = 0.003). However, hip resurfacing had less estimated surgical blood loss (p = 0.005) and less postoperative drain output (p = 0.05), resulting in 252 mL less total blood loss (p = 0.0005) and fewer blood transfusions (p < 0.0001). There was a trend toward a shorter length of stay for the patients undergoing resurfacing (3.3 vs 3.6 days), but the difference was not statistically significant and reflects the presence of several outliers in the

THA group (Table 2).

One patient in the hip resurfacing group was revised for postoperative avascular necrosis (AVN) of the femoral head 17 months postoperatively, and four patients (four hips) in the THA group declined further follow-up and participation in the study, leaving 49 hips in 49 patients in the hip resurfacing group and 40 hips in 31 patients in the THA group. Minimum follow-up was 24 months (mean, 38 months; range, 24 to 50 months) for the hip resurfacing group and 24 months (mean, 30 months; range, 24 to 48 months) for the THA group. The four patients undergoing THA who did not return for formal follow-up were contacted by telephone and stated they had no pain, no problems with their hips, and were not functionally limited by their THA.

Preoperatively, the patients undergoing hip resurfacing had a lower average Harris hip score (46 vs 52 points; p = 0.005), with more pain (94% vs 58%, marked pain; p < 0.0001), but had higher UCLA activity scores (Table 3). Postoperatively, the patients undergoing hip resurfacing demonstrated greater improvement in Harris hip scores (p = 0.002), with an average score of 97, compared to an average of 96 for the THA group. However, fewer patients in the resurfacing group had complete relief of pain (48% vs 80%, pain-free; p = 0.007). The resurfacing group had a 1.5-grade greater increase in UCLA activity score than the THA group (p = 0.003), resulting in a postoperative UCLA activity score of 8.2 versus 5.9 for the THA group (p < 0.0001). Similarly, there was relatively greater improvement in the postoperative function scores (Harris hip score minus the pain, deformity, and ROM components; p = 0.007) and SF-12 physical score (p = 0.002) for the resurfacing group (Table 4).

Both groups demonstrated substantial improvement in postoperative ROM and there were no significant differences in the postoperative ROM between the two groups. However, the patients undergoing THA started with less ROM and had greater improvements with greater increases in flexion, extension, and abduction than the patients undergoing resurfacing (Tables 3 and 4).

Ten patients (14 hips) received a 36-mm metal-metal bearing THA in anticipation of higher postoperative activity. This subset of patients undergoing THA was similar to the resurfacing group, with 62% of these hips (9/14) in male patients; only 30% (9/30) of the metal-on-polyethylene total hips were in males (p = 0.01). The patients with 36-mm metal-metal bearing THA had essentially the same height (68.2 inches), weight (181 pounds), and BMI (27.2 kg/m2) as the patients with an MMSR and were significantly taller (p < 0.0001), leaner (p < 0.0001), and had a higher preoperative UCLA activity score (4.8 vs 2.9; p < 0.0001) than the other patients undergoing THA, with no significant differences in age, diagnoses, or Charnley class.

The postoperative outcome of patients with a 36-mm metal-metal bearing THA was similar to the MMSR group and significantly better than the other patients undergoing THA, with a higher average Harris hip score (99 vs 94; p = 0.05), higher average function score (p = 0.05), higher average SF-12 physical score (563 vs 42; p < 0.0001), higher average SF-12 mental score (57 vs 50; p = 0.007), and a higher average UCLA activity score (7.7 vs 4.9; p < 0.0001). Patients undergoing THA with a 36-mm metal-metal bearing had higher average flexion scores (127 vs 116; p = 0.02) than patients who underwent an MMSR.

There was one femoral failure in the resurfacing group, as mentioned previously. A cementless femoral stem was inserted with a modular femoral head that matched the retained acetabular component. No other component in either group was revised and no component became radiographically loose. In one patient, a small fragment from an inserter attachment slot on the rim of one resurfacing acetabular component broke off (at an indeterminate time) and was demonstrated on a 3-year postoperative radiograph in an asymptomatic patient. One sciatic nerve palsy occurred in the resurfacing group. As well, one posterior dislocation took place in each group; both were managed by closed reduction and were subsequently stable. Brooker (9) Grade I or II heterotopic ossification (HO) occurred in 10 resurfaced hips and four THAs. Two resurfaced hips had Grade III HO. An adverse clinical outcome could not be directly attributed to HO in any of these cases.

Discussion

In the 25 years since total hip resurfacing was last popular in the U.S., there have been technological advances, e.g., cementless fixation and more wear-resistant bearings, which have benefited both resurfacing and THA. Good-to-excellent intermediate-term results have been demonstrated with the current generations of both technologies,2-4,10-13 as was seen in the current study. We hypothesized that the functional benefits of MMSR are due, at least in part, to patient-related variables, such as age and general health status.

The indications for resurfacing are more narrow than those for THA.13 In our study, the majority of patients were relatively young males with osteoarthritis, a group that has historically been at increased risk for failure of a THA. The demographics and outcomes of these MMSR patients are similar to other reported series.2-4 The main limitation of the current study was lack of randomization, which was not possible, because all of the patients undergoing resurfacing were self-referred specifically for that procedure.

The patients undergoing resurfacing were younger, in better general health, and had higher preoperative UCLA activity scores than the patients who underwent a THA. On this basis, it is not surprising the patients undergoing resurfacing had greater improvement in function.

Only 48% of the patients undergoing resurfacing reported complete pain relief, compared with 80% of the patients undergoing THA. An explanation for this may be related to the marked difference in UCLA activity scores (8.2 vs 5.9). The patients undergoing resurfacing generally reported pain only with unusual or extreme activities that most patients undergoing THA do not attempt.

The belief that hip resurfacing provides greater ROM and lower risk for dislocation than THA were not supported by this study. The subset of hips with a 36-mm metal-metal bearing THA actually had higher average postoperative flexion than the resurfaced hips. This is not surprising given that the head-to-neck ratio of a 36-mm head on the conventional hip arthroplasty stem is larger than that of a resurfaced hip. Larger diameter bearings and modular narrowed anteroposterior femoral component necks are functional advances for THA that have become available since resurfacing was last popular.

This experience demonstrated that patients undergoing hip resurfacing differ substantially from patients undergoing conventional THA. It should not, therefore, be unexpected that there are differences in clinical outcomes. By recognizing the differences in the patient groups, caution should be taken in attributing any advantages or limitations directly to either arthroplasty technology. These are timely and valuable perspectives for both surgeons and prospective patients.

Acknowledgment

Each author certifies that his or her institution has approved the human protocol for this investigation, that all investigations were conducted in conformity with ethical principles of research, and that informed consent was obtained.

Disclosure Statement

Financial support for this research study was provided by Wright Medical Technology and the Los Angeles Orthopaedic Hospital Foundation. Thomas P. Schmalzried, M.D., has a financial interest in the total hip replacement prostheses used in this research study (DePuy Pinnacle[TM], Summit[TM], and Ultamet[TM]).

References

(1.) Millennium Research Group. Global Markets for Hip Reconstructive Devices 2002. Toronto: Millennium Research Group, 2002.

(2.) Amstutz HC, Beaule PE, Dorey FJ, et al. Metal-on-metal hybrid surface arthroplasty: two to six-year follow-up study. J Bone Joint Surg Am. 2004;86:28-39.

(3.) Daniel J, Pynsent PB, McMinn DJ. Metal-on-metal resurfacing of the hip in patients under the age of 55 years with osteoarthritis. J Bone Joint Surg Br. 2004;86:177-84.

(4.) Treacy RB, McBryde CW, Pynsent PB. Birmingham hip resurfacing arthroplasty. A minimum follow-up of five years. J Bone Joint Surg Br. 2005;87:167-70.

(5.) Pierce EC Jr. The development of anesthesia guidelines and standards. QRB Qual Rev Bull. 1990;16:61.

(6.) Harris WH. Traumatic arthritis of the hip after dislocation and acetabular fractures: treatment by mold arthroplasty. An end-result study using a new method of result evaluation. J Bone Joint Surg Am. 1969;51:737-55.

(7.) Ware JE, Kosinski M, Keller SD. SF-12: How to Score the SF-12 Physical and Mental Health Summary Scales. (2nd ed). Boston: The Health Institute, New England Medical Center, 1995.

(8.) Amstutz HC, Thomas BJ, Jinnah R, et al. Treatment of primary osteoarthritis of the hip. A comparison of total joint and surface replacement arthroplasty. J Bone Joint Surg Am. 1984;66:228-41.

(9.) Booker AF, Bowerman JW, Robinson RA, Riley LH Jr. Ectopic ossification following total hip replacement. Incidence and a method of classification. J Bone Joint Surg Am. 1973;55:1629-32.

(10.) D'Antonio J, Capello W, Manley M, et al. Alumina ceramic bearings for total hip arthroplasty: five-year results of a prospective randomized study. Clin Orthop Relat Res. 2005;(436):164-71.

(11.) Long WT, Dorr LD, Gendelman V. An American experience with metal-on-metal total hip arthroplasties. A 7-year followup study. J Arthroplasty. 2004;19(Suppl 3):29-34.

(12.) Migaud H, Jobin A, Chantelot C, et al. Cementless metal-onmetal hip arthroplasty in patients less than 50 years of age. Comparison with a matched control group using ceramicon-polyethylene after a minimum of 5-year follow-up. J Arthroplasty. 2004;19(Suppl 3):23-8.

(13.) Schmalzried TP, Silva M, dela Rosa M, et al. Optimizing patient selection and outcomes with total hip resurfacing. Clin Orthop Relat Res. 2005;(441):200-4.

Vincent A. Fowble, M.D., Mylene A. dela Rosa, B.S., C.C.R.P., and Thomas P. Schmalzried, M.D. Vincent A. Fowble, M.D., Mylene A. dela Rosa, B.S., C.C.R.P., and Thomas P. Schmalzried, M.D., are from Joint Replacement Institute, St. Vincent Medical Center, Los Angeles, California.

Correspondence: Thomas P. Schmalzried, M.D., Joint Replacement Institute at St. Vincent Medical Center, 2200 West Third Street, Los Angeles, California 90057-0992; schmalzried@earthlink.net.
Table 1 Demographics

                       MMSR               THA
                       (50 hips/50        (44 hips/35
Demographic            patients)          patients)          P-Value

Gender                 Male: 31 (62%)     Male: 18 (41%)
                       Female: 19 (38%)   Female: 26 (59%)   0.03
Age (years)            46                 55                 0.0001
Range                  30-64              27-75
Height (inches)        68.7               65.5               0.0001
Range                  62-76              59-71
Weight (pounds)        183.6              190.5              0.4
Range                  114-277            106-262
Body mass index        27.3               31.3               0.0009
Range                  20.5-44.8          19.5-42.3
Charnley Class         A. 41 (82%)        21 (48%)
                       B. 8 (16%)         22 (50%)           0.001
                       C. 1 (2%)          1 (2%)
Diagnosis              OA: 48 (96%)       OA: 40 (91%)
                       ON: 1 (2%)         ON: 3 (7%)
                       Other: 1 (2%)      Other: 1 (2%)
American Society of    1.27 (54%)         8 (18%)
Anesthesiologists      2.19 (38%)         27 (61%)           0.001
Class                  3. 4 (8%)          9 (20%)

MMSR = metal-metal surface replacement; OA = osteoarthritis; ON =
osteonecrosis

Table 2 Perioperative Data

                             MMSR                             THA
                          (50 hips/                        (44 hips/
                         50 patients)                     35 patients)

Event          Average      Range        SD     Average      Range

Anesthesia       242       175-485       47       199       120-350
  time
(minutes)
Surgery          174       105-410       46       148       100-280
  time
  (minutes)
Estimated        456       200-1500     216.8     618       150-1700
  blood
  loss (mL)
Hemovac (mL)     263        0-725       167.3     353        0-1425
Total blood      719       300-1780     268.9     971       200-2225
  loss (mL)
Transfusions   Yes: 12                          Yes: 28
                (24%)                            (64%)
               No: 38                           No: 16
                (76%)                            (36%)
Hospital         3.3         2-4         0.6      3.6         2-9
  stay
  (days)

Event           SD     Difference   P-Value

Anesthesia      42         43       <0.0001
  time
(minutes)
Surgery         33         26        0.003
  time
  (minutes)
Estimated      321.9      -162       0.005
  blood
  loss (mL)
Hemovac (mL)   272.8      -90         0.05
Total blood    405.0      -252       0.0005
  loss (mL)
Transfusions                         0.0001

Hospital        1.0       -0.3        0.06
  stay
  (days)

MMSR = metal-metal surface replacement; SD = standard
deviation

Table 3 Preoperative Clinical Data

                 MMSR                       THA
                 (50 hips/50 patients)      (44 hips/35 patients)

Measure          Average Range       SD     Average Range        SD

Harris hip       46      25-59       9      52      30-73        11
  score
University of    4.2     2-7         1.1    3.6     2-7          1.4
  California
  at Los
  Angeles
  activity
  score
Short Form-12    33.6    21.2-52.9   8.4    25.8    24.7-27.0    1.6
  physical
  score
Short Form-12    44.2    13.2-65.4   12.8   35.2    24.0-46.4    15.8
  mental score
Function         27.3    7-39        8.3    29.9    12-47        7.4
Pain             Moderate: 3 (6%)           Moderate: 17 (42%)
                 Marked: 47 (94%)           Marked: (58%)
Flexion          95      45-125      15     80      0-120        23
Extension        -9      -25-0       7      -5      -30-15       10
Abduction        27      0-45        11     15      0-40         15
Adduction        8       -20-20      10     2       0-20         5
IR               -4      -30-30      14     -2      -30-20       12
ER               25      0-45        10     20      0-40         12

Measure          Difference   P-Value

Harris hip       -6           0.005
  score
University of    0.6          0.02
  California
  at Los
  Angeles
  activity
  score
Short Form-12    7.8          0.2
  physical
  score
Short Form-12    9.0          0.3
  mental score
Function         -2.6         0.1
Pain                          0.0001

Flexion          15           0.0001
Extension        -4           0.03
Abduction        12           0.0001
Adduction        6            0.0003
IR               -2           0.5
ER               5            0.03

MMSR = metal-metal surface replacement; SD = standard deviation; IR
= internal rotation; ER = external rotation

Table 4 Postoperative Clinical Data

                 MMSR                        THA
                 (49 hips/49 patients)       (40 hips/31 patients)

Measure          Average   Range       SD    Average   Range       SD

Harris hip       97        81-100      4     96        66-100      7
  score
University of    8.2       4-10        1.6   5.9       3-10        1.7
  California
   at Los
   Angeles
  activity
  score
Short Form-12    53.6      36.9-63.0   5.9   47.0      15.2-57.6   13.1
  physical
  score
Short Form-12    54.6      26.7-61.7   6.7   52.5      32.1-66.6   9.1
  mental score
Function         46.4      42-47       1.4   44.9      36-47       3.3
Pain             None: 28 (57%)              None: 32 (80%)
                 Slight: 18 (37%)            Slight: 6 (15%)
                 Mild: 3 (6%)                Moderate: 2 (5%)
Flexion          116       90-160      14    119       90-170      18
Extension        6         -15-60      14    1         -10-25      7
Abduction        46        30-70       10    45        25-70       12
Adduction        22        10-60       10    19        0-45        10
IR               27        0-90        16    25        0-60        16
ER               42        20-80       12    41        20-70       11

Measure          Difference   P-Value

Harris hip       1            0.4
  score
University of    2.3          0.0001
  California
   at Los
   Angeles
  activity
  score
Short Form-12    6.6          0.002
  physical
  score
Short Form-12    2.1          0.2
  mental score
Function         1.5          0.007
Pain                          0.007

Flexion          -3           0.4
Extension        5            0.08
Abduction        1            0.7
Adduction        3            0.1
IR               2            0.6
ER               1            0.7

MMSR = metal-metal surface replacement; SD = standard
deviation; IR = internal rotation; ER = external rotation
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