Abstract
Background
When positioning the acetabular component for total hip arthroplasty (THA) in patients with sequelae of Legg-Calvé-Perthes disease (LCPD), elevating the center of rotation (COR) of the hip is often unavoidable. We aimed to compare the outcomes between the preserved and elevated COR groups in patients with sequelae of LCPD.
Methods
We enrolled 53 patients who underwent primary THA for sequelae of LCPD between 2006 and 2019. Patients were divided into 2 groups based on the postoperative COR position: 19 in the preserved COR group and 34 in the elevated COR group. The mean elevation of COR was 2.7 mm (range, 0–5.0 mm) in the preserved COR group and 8.1 mm (range, 6.0–12.0 mm) in the elevated COR group. Radiological outcomes, such as osteolysis and implant loosening, were evaluated. Additionally, reoperation, perioperative complications, limping gait, pelvic obliquity, and the modified Harris hip score (mHHS) were assessed.
Results
There were no significant differences in radiological or clinical outcomes between the 2 groups. Neither osteolysis nor implant loosening was observed, and no reoperations were required. Intraoperative periprosthetic femoral fractures occurred in 3 cases (6%), but no cases of sciatic nerve palsy were observed. Residual limping gait was noted in 10 patients (19%), and pelvic obliquity persisted in 8 patients (15%). At the last follow-up, the mean mHHS was 89.2.
Conclusions
The 5–17-year follow-up results of primary cementless THA in patients with sequelae of LCPD were satisfactory. Furthermore, a moderate elevation of the COR, with a mean of 8.1 mm (range, 6.0–12.0 mm), did not significantly affect the outcomes of THA in these patients. Therefore, a moderate elevation of the COR can be considered an acceptable option for patients undergoing THA with sequelae of LCPD.
Keywords: Total hip arthroplasty, Legg-Calvé-Perthes disease, Center of rotation
Among all patients undergoing total hip arthroplasty (THA) due to hip osteoarthritis, the incidence of secondary osteoarthritis as a sequela of Legg-Calvé-Perthes disease (LCPD) is reported to be approximately 0.6%–4.2%.1,2) THA for sequelae of LCPD is more complicated and technically challenging than primary THA due to characteristic deformities of the proximal femur and dysplasia of the acetabulum.3) Characteristic deformities of the proximal femur, such as coxa magna and coxa breva, may require a special design of the femoral stem, making horizontal offset restoration challenging. Additionally, several challenges can occur, including the postoperative incomplete recovery of leg length discrepancy (LLD), neurological injury due to excessive limb lengthening, and intraoperative periprosthetic fracture.1,4,5)
In patients with sequelae of LCPD, acetabular dysplasia is mostly observed due to the deformed femoral head. When positioning the acetabular component for THA, medialization and elevation of the center of rotation (COR) of the hip is often inevitable to maximize host bone contact. Moreover, the elevation of COR is closely related to the long-term survival of THA and the abductor muscle function.6,7) Other factors, such as an abnormal anteversion angle of the acetabulum and contracture of the surrounding soft tissues, make surgery challenging in patients with sequelae of LCPD, raising concerns regarding long-term survival. However, few studies have reported on THA in patients with sequelae of LCPD, with varying results.5,8,9) Furthermore, research on the follow-up results according to the degree of COR elevation in such patients is scarce. Therefore, this study aimed to analyze the clinical and radiological outcomes of primary THA in patients with sequelae of LCPD. Moreover, we divided the study cases into 2 groups based on the postoperative position of COR (elevated or preserved group) and assessed for differences in outcomes between these groups. We hypothesized that the results of THA in these patients would be satisfactory and anticipated that an elevated COR would negatively impact the outcomes.
METHODS
This study was conducted in accordance with the Declaration of Helsinki. The study protocol was reviewed and approved by the Institutional Review Board of Pusan National University Yangsan Hospital (IRB No. 55-2024-047), and the requirement for informed consent was waived.
This single-center, retrospective comparative cohort study enrolled patients who underwent primary THA between March 2006 and March 2019 at our tertiary university hospital. The inclusion criteria for this study comprised patients who underwent primary THA for sequelae of LCPD with secondary osteoarthritis with a minimum follow-up of 5 years. Two patients were lost to follow-up. Ten patients were further excluded due to insufficient follow-up visits or incomplete medical records. Ultimately, 53 hips with a minimum follow-up of 5 years were included in the study. Patients were divided into 2 groups based on the position of the postoperative COR of the hip. The first group, preserved COR, included cases in which the COR was maintained within 5 mm of the contralateral side.10) In contrast, the second group, elevated COR, included cases in which the COR was elevated > 5 mm. The preserved and elevated COR groups included 19 cases and 34 cases, respectively (Fig. 1). The mean elevation of COR was 2.7 mm (range, 0–5.0 mm) in the preserved COR group and 8.1 mm (range, 6.0–12.0 mm) in the elevated COR group.
Fig. 1. Study flowchart. THA: total hip arthroplasty, LCPD: Legg-Calvé-Perthes disease, COR: center of rotation.
Age, sex, body mass index, bone mineral density, comorbidities, laterality, and American Society of Anesthesiologists status were not different between the groups. The mean follow-up period was 5.7 years (p = 0.600), with no difference between the groups. The mean preoperative flexion contracture was 12.3° (p = 0.759), with no difference between the groups. Preoperative LLD averaged –22.2 mm (negative values indicate shorter length compared to the opposite side), showing a greater discrepancy in the elevated COR group (p = 0.004) (Table 1).
Table 1. Preoperative Demographics.
| Variable | Total | Preserved COR | Elevated COR | p-value | |
|---|---|---|---|---|---|
| Number | 53 | 19 | 34 | - | |
| Age (yr) | 50.0 ± 12.0 | 48.2 ± 13.7 | 51.4 ± 11.5 | 0.369 | |
| Sex | 0.887 | ||||
| Female | 30 (57) | 11 (58) | 19 (56) | ||
| Male | 23 (43) | 8 (42) | 15 (44) | ||
| BMI (kg/m2) | 24.2 ± 3.3 | 24.2 ± 3.4 | 24.2 ± 3.3 | 0.996 | |
| BMD (T-score) | –0.3 ± 1.3 | –0.5 ± 1.4 | –0.2 ± 1.3 | 0.363 | |
| Follow-up (yr) | 5.7 ± 4.1 | 5.3 ± 3.8 | 6.0 ± 1.3 | 0.600 | |
| Comorbidity | |||||
| Diabetes | 3 (6) | 0 | 3 (9) | 0.545* | |
| Hypertension | 6 (11) | 3 (16) | 3 (9) | 0.655* | |
| Dyslipidemia | 3 (6) | 0 | 3 (9) | 0.545* | |
| Angina | 2 (4) | 2 (11) | 0 | 0.124* | |
| Atrial fibrillation | 1 (2) | 0 | 1 (3) | 1.000* | |
| Cerebrovascular accident | 2 (4) | 2 (11) | 0 | 0.124* | |
| Venous thromboembolism | 1 (2) | 0 | 1 (3) | 1.000* | |
| Hepatitis | 1 (2) | 0 | 1 (3) | 1.000* | |
| Solid organ cancer | 1 (2) | 0 | 1 (3) | 1.000* | |
| Hypothyroidism | 1 (2) | 1 (5) | 0 | 0.358* | |
| Laterality | 0.854* | ||||
| Right | 23 (43) | 8 (42) | 15 (44) | ||
| Left | 30 (57) | 11 (58) | 19 (56) | ||
| Bilateral, person | 6 | 3 | 3 | ||
| ASA score | |||||
| I | 33 (62) | 10 (53) | 23 (67) | 0.377* | |
| II | 18 (34) | 9 (47) | 9 (26) | 0.143* | |
| III | 2 (4) | 0 (0) | 2 (7) | 0.531* | |
| Flexion contracture (°) | 12.3 ± 7.4 | 11.8 ± 6.5 | 12.5 ± 7.9 | 0.759 | |
| Preoperative mHHS | 47.9 ± 9.2 | 48.3 ± 8.1 | 46.7 ± 10.2 | 0.699 | |
| Surgical approach | |||||
| Posterolateral | 53 (100) | 19 (100) | 34 (100) | 1.000 | |
| Preoperative LLD (mm) | –22.2 ± 9.0 | –17.6 ± 8.5 | –24.9 ± 8.3 | 0.004 | |
Values are presented as mean ± standard deviation or number (%).
COR: center of rotation, BMI: body mass index, BMD: bone mineral density, ASA: American Society of Anesthesiologists, mHHS: modified Harris hip score, LLD: leg length discrepancy.
*Fisher’s exact test.
All operations were performed by an experienced arthroplasty surgeon (WCS) using a posterolateral approach in the lateral decubitus position. For all patients, the appropriate cup position and the extent of bone grafting were predicted by preoperative templating. Cup placement was aimed at restoring the anatomical COR where possible. In cases of insufficient contact or coverage between the host bone and the cup, medialization and elevation of the COR were allowed (Fig. 2). However, when the elevation of the COR > 15 mm was anticipated based on preoperative templating, a strut bone graft was considered. Moreover, when a strut or cancellous bone graft was needed to restore the COR and fill the defect site, femoral head allografts, which were frozen and stored at –80 ℃ after collection and radiation sterilization at a dose of 25 kGy, were prepared to achieve cup positioning. A strut bone graft (Fig. 3) was required in 7 cases, and it was more commonly performed in the preserved COR group (5 cases, p = 0.084) (Table 2). In addition, a preoperative computed tomography scan was performed on all patients, and the images obtained were used to assess the degree of acetabulum and femur deformation.
Fig. 2. Preoperative templating images. (A) Preserved center of rotation (COR). (B) Elevated COR.
Fig. 3. A postoperative radiograph showing a strut bone graft used to preserve the center of rotation.
Table 2. Operative Data.
| Parameter | Total (n = 53) | Preserved COR (n = 19) | Elevated COR (n = 34) | p-value | |
|---|---|---|---|---|---|
| Acetabular component | |||||
| G7 (Zimmer Biomet) | 32 (60) | 11 (58) | 21 (62) | 0.782 | |
| Trilogy (Zimmer Biomet) | 18 (34) | 5 (26) | 13 (38) | 0.380 | |
| Continuum (Zimmer Biomet) | 2 (4) | 2 (11) | 0 | 0.124* | |
| MIRABO (CorenTec) | 1 (2) | 1 (5) | 0 | 0.358* | |
| Cup size (mm) | 50.8 ± 3.1 | 50.2 ± 4.0 | 51.1 ± 2.5 | 0.159 | |
| Acetabular anteversion (°) | 1.3 ± 9.0 | 1.4 ± 7.4 | 1.3 ± 9.9 | 0.961 | |
| Cup anteversion (°) | 18.7 ± 4.8 | 19.3 ± 5.0 | 18.3 ± 4.8 | 0.464 | |
| Cup inclination (°) | 44.0 ± 1.0 | 44.6 ± 1.2 | 44.4 ± 1.5 | 0.580 | |
| Postoperative COR (mm) | 6.2 ± 3.2 | 2.7 ± 1.9 | 8.1 ± 1.9 | 0.031 | |
| Transacetabular screw | |||||
| 0 | 4 (8) | 1 (5) | 3 (9) | 1.000* | |
| 1 | 42 (79) | 14 (74) | 28 (82) | 0.456 | |
| 2 | 7 (13) | 4 (21) | 3 (9) | 0.234* | |
| Bearing liner | |||||
| Longevity (Zimmer Biomet) | 19 (36) | 6 (32) | 13 (38) | 0.628 | |
| E1 fixed (Zimmer Biomet) | 7 (13) | 3 (16) | 4 (12) | 0.691* | |
| E1 dual mobility (Zimmer Biomet) | 25 (47) | 8 (42) | 17 (50) | 0.581 | |
| Ceramic (Biolox delta, CeramTec) | 2 (4) | 2 (10) | 0 | 0.124* | |
| Femoral component | |||||
| Versys FMT (Zimmer, Biomet) | 26 (49) | 10 (53) | 16 (47) | 0.779* | |
| Microplasty (Zimmer, Biomet) | 22 (41) | 8 (42) | 14(41) | 1.000* | |
| Wager cone (Zimmer, Biomet) | 3 (6) | 0 | 3 (9) | 0.545* | |
| Bencox II (CorenTec) | 2 (4) | 1 (5) | 1 (3) | 1.000* | |
| Postoperative femoral offset (mm) | –2.8 ± 6.8 | –2.6 ± 5.7 | –2.8 ± 7.4 | 0.923 | |
| Change of femoral offset (mm) | 5.7 ± 3.4 | 6.7 ± 3.5 | 5.2 ± 3.2 | 0.129 | |
| Prosthetic femoral head | 0.290* | ||||
| Ceramic (Biolox delta, CeramTec) | 50 (94) | 17 (89) | 33 (97) | ||
| Cobalt-chromium | 3 (6) | 2 (11) | 1 (3) | ||
| Femoral head size (mm) | 0.871 | ||||
| 28 | 40 (75) | 15 (79) | 25 (74) | ||
| 32 | 9 (17) | 3 (16) | 6 (18) | ||
| 36 | 4 (8) | 1 (5) | 3 (9) | ||
| Strut graft | 7 (13) | 5 (26) | 2 (6) | 0.084* | |
| Tenotomy including adductors and flexors | 18 (34) | 7 (37) | 11 (32) | 0.770* | |
| Operative time (min) | 78.1 ± 24.2 | 83.2 ± 35.6 | 75.3 ± 14.2 | 0.260 | |
| Postoperative LLD (mm) | –4.4 ± 5.3 | –2.1 ± 2.6 | –5.7 ± 5.9 | 0.003 | |
| Lengthening (mm) | 17.4 ± 6.8 | 15.4 ± 7.0 | 18.9 ± 6.5 | 0.071 | |
Values are presented as number (%) or mean ± standard deviation.
COR: center of rotation, LLD: leg length discrepancy.
*Fisher’s exact test.
A cementless acetabular cup was used in all patients. The acetabular cups used were the G7 (Zimmer Biomet), Trilogy (Zimmer Biomet), Continuum (Zimmer Biomet), or MIRABO (Corentec). In most cases, due to the presence of acetabular dysplasia, sufficient medialization was performed to fix the cup using the press fitting technique. The average size of the acetabular cup used was 50.8 ± 3.1 mm, with no difference between the groups. The highly cross-linked polyethylene liners used were Longevity (Zimmer Biomet) for the Trilogy cup, E1 (Zimmer Biomet): Vitamin E-infused polyethylene for the G7 cup, and Biolox Delta liner (CeramTec AG) for Continuum and MIRABO cups. All femoral stems used were cementless. Depending on the shape of the proximal femur and the medullary canal, various stems were employed, including the Versys FMT (Zimmer Biomet), Microplasty (Zimmer Biomet), Wagner cone (Zimmer Biomet), and Bencox II (Corentec) stems. The femoral head used was the ceramic head (Biolox Delta, CeramTec) in 50 cases (94%). The femoral head size was 28 mm in 40 cases (75%), 32 mm in 9 cases (17%), and 36 mm in 4 cases (8%). The frequency of usage of all types of implants was not different between the groups (Table 2).
After inserting the final implants, an additional tenotomy was performed if tightness was still observed after soft-tissue release. A partial tenotomy of the iliopsoas and rectus femoris was performed if flexion contracture remained. Moreover, an additional adductor tenotomy was performed if there was significant adductor tightness compared to the contralateral side after changing to the supine position. Intraoperative tenotomy was performed in 18 cases, with no differences between the groups (Table 2). On the second postoperative day, the patients were instructed to walk with partial weight-bearing, with the aid of crutches or walkers, with full weight-bearing as tolerated. The postoperative rehabilitation methods were not different between the groups.
A postoperative radiological review was performed at 6 weeks, 3, 6, and 12 months, and annually thereafter. PolyWare 7 (Draftware Developers Inc.) was used to measure the anteversion and inclination of the acetabular cup.11) Postoperative acetabular cup anteversion averaged 18.7° ± 4.8° and inclination averaged 44.0° ± 1.0°, with no between-group differences. Standard radiographs, with additional Judet views, were used to detect periprosthetic osteolysis. Radiolucent lesions ≥ 2 mm around the prosthetic components that were not present immediately postoperatively denoted osteolysis.12) Changes in the inclination > 5° and vertical or horizontal migration of the acetabular component ≥ 2 mm were defined as acetabular component loosening.13)
We checked the anticipated leg lengthening and femoral neck cutting level through preoperative templating. The maximum leg lengthening was set to 20 mm to minimize the risk of sciatic nerve palsy. During surgery, leg lengthening was measured using an intraoperative ruler by assessing the distance of the line between the marked vastus ridge and the marked pelvic bone, which passes through the hip center. A mean postoperative LLD of –4.4 ± 5.3 mm compared to the unaffected side was noted, with a mean lengthening of 17.4 mm. The postoperative LLD was significantly greater in the elevated COR group (p = 0.003). The degree of postoperative lengthening did not differ between the groups. We evaluated the COR position in comparison to the unaffected contralateral hip and assessed the differences in vertical COR using images obtained immediately postoperatively (Fig. 4). If the contralateral hip was abnormal, we used the Ranawat triangle method to determine the approximate center of the femoral head.14) Moreover, we compared the postoperative femoral offset with the unaffected contralateral hip. The postoperative mean difference in femoral offset was –2.8 mm compared to the unaffected side, with no differences between the groups. Femoral offset was measured using the Sundsvall method,15) defined as the horizontal distance between the pelvic midline and the femoral axis at the level of the most lateral border of the greater trochanter. The mean difference in femoral offset between the preoperative and postoperative states was 5.7 mm, with no statistically significant difference observed between the groups (p = 0.129) (Table 2).
Fig. 4. Illustration of the method used to measure the difference in the center of rotation (COR) position compared to the anatomical COR of the unaffected contralateral hip.
Patient medical records and radiographs were analyzed to assess reoperation and perioperative complications, including dislocation, periprosthetic fracture, heterotopic ossification, deep joint infection, and sciatic nerve palsy. Additionally, during the follow-up, the presence of a limping gait and remaining pelvic obliquity were investigated. At 1 year postoperatively, pelvic obliquity was measured as the angle between the horizontal plane and the inter-teardrop line. Pelvic obliquity > 5° was defined as remaining pelvic obliquity.16) The hospital stay of the 2 groups was investigated. The modified Harris hip score (mHHS) was used to assess the patient-reported outcomes.
Statistical Analysis
Summary data are expressed as means ± standard deviations for continuous variables and as numbers and frequencies (%) for categorical variables. Continuous variables with a non-normal distribution were analyzed using the Mann-Whitney U-test, whereas those with a normal distribution were analyzed using independent t-tests. Categorical data were statistically analyzed using the chi-square or Fisher&s exact test (n < 40 or t < 1). Statistical analysis was performed using SPSS software version 24.0 (IBM Corp.). A p < 0.05 was considered statistically significant.
RESULTS
There were no significant differences in radiological or clinical outcomes between the groups (Table 3). Neither osteolysis nor implant loosening was observed in any of the 53 patients until the last follow-up, and no reoperations were required. Perioperative complications were observed in 5 cases (9%) with no significant differences between the groups, including intraoperative periprosthetic femoral fractures in 3 cases (6%) and postoperative heterotopic ossification (Brooker type I) in 2 cases (4%). No postoperative dislocations, deep infections, or sciatic nerve palsy were observed in either group. A persistent limping gait was observed in 10 cases (19%), with no differences between the groups (p = 1.000). Pelvic obliquity was not corrected and persisted in 8 cases (15%), with no differences between the groups (p = 0.696). The mean hospital stay was 9.8 days, showing no significant difference (p = 0.909). The mean mHHS at the last follow-up was 89.2, with no significant differences between the groups (p = 0.712) (Table 3).
Table 3. Postoperative Outcomes.
| Parameter | Total (n = 53) | Preserved COR (n = 19) | Elevated COR (n = 34) | p-value | |
|---|---|---|---|---|---|
| Radiologic outcome at the last FU | |||||
| Osteolysis | 0 | 0 | 0 | 1.000* | |
| Implant loosening | 0 | 0 | 0 | 1.000* | |
| Reoperation | 0 | 0 | 0 | 1.000* | |
| Complications | |||||
| Dislocation | 0 | 0 | 0 | 1.000* | |
| Intraoperative periprosthetic fracture | 3 (6) | 0 | 3 (9) | 0.545* | |
| Heterotopic ossification | 2 (4) | 0 | 2 (6) | 0.531* | |
| Deep joint Infection | 0 | 0 | 0 | 1.000* | |
| Sciatic nerve palsy | 0 | 0 | 0 | 1.000* | |
| Limping gait | 10 (19) | 3 (16) | 7 (21) | 1.000* | |
| Remaining pelvic obliquity | 8 (15) | 2 (11) | 6 (18) | 0.696* | |
| Hospital stay (day) | 9.8 ± 3.0 | 9.9 ± 3.0 | 9.8 ± 2.6 | 0.909 | |
| mHHS at the last FU | 89.2 ± 8.9 | 90.1 ± 7.4 | 88.1 ± 10.2 | 0.712 | |
Values are presented as number (%) or mean ± standard deviation.
COR: center of rotation, FU: follow-up, mHHS: modified Harris hip score.
*Fisher’s exact test.
DISCUSSION
In our study, although we noted a high complication rate of intraoperative periprosthetic fractures (3 cases, 6%), we observed satisfactory implant survival with no reoperations in patients with sequelae of LCPD at a follow-up of over 5 years. Several studies have also demonstrated outcomes of primary THA in patients with sequelae of LCPD with high overall rates of complications, including a high incidence of intraoperative periprosthetic fracture and sciatic nerve palsy.1,3,5) Baghdadi et al.1) reviewed primary THAs performed in 95 patients with a history of LCPD. Cementless THAs for the sequelae of LCPD demonstrate 90% survival from any revision at 8-year follow-up. Complications occurred in 16% including 9 intraoperative fractures (9%) and 3 sciatic nerve palsies (3%). Traina et al.3) assessed the results of 32 THAs in LCPD retrospectively. The cumulative survival rate at 15 years was 96.9%. The overall rate of complications was 12.5%, with 2 permanent sciatic nerve palsies (6%). Hanna et al.5) carried out a systematic review of the literature involving 245 THAs in patients with LCPD. There were 16 revision THAs (7%) occurring at a mean of 7.5 years. Complications included 27 intraoperative fractures (11%), 13 cases of aseptic loosening (5%), and 7 sciatic nerve palsies (3%). However, prior studies have not analyzed the outcomes based on the degree of COR elevation following THA in patients with sequelae of LCPD. In patients with sequelae of LCPD, the acetabulum often exhibits dysplasia matching the femoral deformity. For acetabular dysplasia, adequate medialization is necessary for contact with the host bone and cup coverage, and in severe cases, an elevated COR is unavoidable.17) We hypothesized that an elevated COR would negatively impact the outcomes and compared the outcomes between the preserved and elevated groups. However, the comparison between the groups based on moderate COR elevation (range, 6.0–12.0 mm) did not show a significant difference.
Although an elevated COR may simplify surgery, excessive elevation (> 15 mm) has been associated with reduced implant longevity and adverse effects on abductor muscle function.6,7,18,19) Elevation of more than 15 mm above the anatomical center of the femoral head has been linked to increased rates of loosening and revision of both femoral and acetabular components.20) However, the acetabular dysplasia observed in patients with LCPD is generally less severe than that seen in patients with developmental dysplasia of the hip; therefore, elevation of the COR beyond 15 mm is rarely necessary. Furthermore, strut bone grafts were utilized in cases where preoperative templating predicted a COR elevation greater than 15 mm. While strut bone grafts pose challenges such as resorption during long-term follow-up and increased surgical complexity,21) they are infrequently needed in patients with sequelae of LCPD for COR restoration. For these reasons, we believe our results were satisfactory, with no significant differences observed between the groups.
Another issue in patients with sequelae of LCPD is LLD. Although it is primarily due to bone deformity, as the disease occurs in childhood, surrounding soft tissues are also tight and inflexible, making sufficient leg lengthening often impossible. Excessive lengthening during THA portends contracture and nerve injury.4,8) In this study, we aimed to avoid lengthening > 20 mm, and fortunately, no nerve injuries were observed postoperatively. This was attributed to thorough preoperative templating and adequate intraoperative release of soft tissues. Postoperative residual LLD averaged –4.4 mm, unlikely to cause significant discomfort in daily life.22)
This study has some limitations. First, this was a retrospective single-center study involving consecutive patients treated by a single surgeon. Second, the sample size was relatively small, which may have limited the statistical power to detect significant differences between groups. While LCPD is a rare condition and THA is typically reserved for adults with advanced secondary osteoarthritis, the limited number of cases increases the risk of type II error. Post hoc power analysis could not be meaningfully performed for several key outcomes, such as implant loosening, due to the absence of events in both groups. As a result, the lack of statistically significant differences should be interpreted with caution. Larger-scale studies are needed to validate these findings and clarify the clinical impact of COR elevation. Third, various types of implants were used depending on the femur shape. However, cases were not enough to categorize and compare based on the implant type. As the composition of implants was not significantly different between the groups, it presumably did not impact the results significantly. Fourth, there were significant differences in mean preoperative and postoperative LLD between the groups. We believe that the elevated COR group exhibited greater LLD due to more deformities. Since we aimed to avoid lengthening beyond 20 mm and the degree of lengthening did not significantly differ between the groups, this resulted in a significant difference in postoperative LLD between the groups. However, we do not consider this difference to be clinically meaningful. According to several studies,23,24) LLDs of 10 mm or more are typically recognized by the majority of individuals and are associated with discomfort, whereas discrepancies below this threshold are often well tolerated. In our study, both groups had mean postoperative LLD values below 10 mm (–2.1 mm vs. –5.7 mm), supporting the interpretation that the observed difference, although statistically significant, is unlikely to be clinically relevant. Fifth, the follow-up period was relatively short, necessitating continuous observation for long-term results. Finally, abductor function was not evaluated in this study. Although a limping gait can result from various factors, it is strongly influenced by abductor muscle function. In our cohort, there was no statistically significant difference in the incidence of postoperative limping gait between the groups (p = 1.000) (Table 3). However, to more precisely determine the effect of COR elevation on functional outcomes, future studies should incorporate objective assessments of abductor muscle strength or function.
The 5- to 17-year follow-up results of primary cementless THA in patients with sequelae of LCPD were satisfactory. Furthermore, a moderate elevation of the COR, with a mean of 8.1 mm (range, 6.0–12.0 mm), did not significantly affect the outcomes of THA in these patients. Therefore, a moderate elevation of the COR can be considered an acceptable option for patients undergoing THA with sequelae of LCPD.
ACKNOWLEDGEMENTS
This study was supported by Research Institute for Convergence of Biomedical Science and Technology (30-2024-003), Pusan National University Yangsan Hospital.
Footnotes
CONFLICT OF INTEREST: No potential conflict of interest relevant to this article was reported.
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