Outcome of Ceramic-on-Ceramic Total Hip Arthroplasty with 4th Generation 36 mm Head Compared to that with 3rd Generation 28 mm Head by Propensity Score Matching

Abstract

Background

With the development of 4th generation ceramic bearing, the large ceramic head is available for ceramic-on-ceramic total hip arthroplasty (THA). This retrospective study aimed to compare the outcomes of ceramic-on-ceramic THA with 4th generation 36 mm head to those with 3rd generation 28 mm head using propensity score matching.

Methods

We retrospectively reviewed the results of 133 ceramic-on-ceramic THAs with 4th generation 36 mm ceramic head in 129 patients and 133 ceramic-on-ceramic THAs identified from 405 ceramic-on-ceramic THAs with 3rd generation 28 mm head by propensity score matching. There were 83 males and 50 females in both groups with a mean age of 55 years. There was no significant difference in other demographic features except for follow-up period (4.2 years in the 36 mm group and 6.4 years in the 28 mm group, p < 0.001). Clinical and radiological results and occurrence of complication were compared between the two groups.

Results

Harris Hip Score was increased significantly from 46.4 to 92.1 in the 36 mm group and from 46.7 to 93.6 in the 28 mm group. No loosening or osteolysis was observed in the 36 mm group. However, one hip showed radiologic sign of loosening in the 28 mm group. As for complication, postoperative dislocation was more frequent in the 28 mm group (6 in the 28 mm group vs. 0 in the 36 mm group, p = 0.03). Otherwise, there was no significant difference in other results including inguinal pain, squeaking or ceramic fracture.

Conclusion

Ceramic-on-ceramic THA with 4th generation 36 mm head significantly reduced postoperative dislocation rate without increasing the rate of inguinal pain, squeaking, or ceramic fracture compared to that with 3rd generation 28 mm head.

Introduction

Postoperative dislocation is one of the most serious complications of total hip arthroplasty (THA) [1, 2]. Recurrent dislocation is one leading cause of revision THA [3]. The small size of the prosthetic head is a well-known risk factor for dislocation [2]. The large femoral head could reduce the rate of dislocation after THA with increased jumping distance and appropriate soft tissue tension [2]. Several studies have shown that postoperative dislocation rate can be reduced with large head compared to conventional-sized head [4, 5].

However, there are some concerns about hip replacement with large metal head [6]. Large femoral head could irritate psoas tendon and result in unexpected inguinal pain [7]. Metal-on-metal THA with large head might cause pseudotumor formation [8]. Recently, increased rate of tribocorrosion in taper junction has been reported to be associated with the large metal head [9]. Moreover, volumetric wear of polyethylene liner is increased when it is coupled with the large metal head [6, 10].

The ceramic-on-ceramic THA has extreme wear resistance with excellent results [11]. However, ceramic fracture and squeaking are unique complications of ceramic-on-ceramic THA due to characteristics of biomaterial [2, 12, 13]. Previously, the head size has been limited to 28 mm or 32 mm in 3rd generation ceramic-on-ceramic THA due to concerns about ceramic liner fracture. However, after introduction of the 4th generation ceramic with the better mechanical property, the thickness of the liner could be minimized [14, 15]. The larger sized head is now available with decreased concern about ceramic liner fracture [14]. Recent clinical studies have shown favorable results of THAs with 4th generation ceramic bearings with excellent implant survival and reduced rates of ceramic head fracture [16–18].

Despite favorable results of 4th generation ceramic-on-ceramic THAs, concerns about ceramic liner fracture and squeaking remain [14, 15]. Compared to the large metal head, problems associated with large ceramic head have not been well established yet in ceramic-on-ceramic THA. This retrospective study aimed to evaluate ceramic-on-ceramic THA with 4th generation 36 mm head regarding the occurrence of dislocation and complication related to large ceramic femoral head, including ceramic bearing fracture, inguinal pain, and squeaking. We compared the outcomes of ceramic-on-ceramic THA with 4th generation 36 mm head and those with 3rd generation 28 mm head using one-to-one propensity score matching.

Materials and Methods

From July 2010 to December 2013, 212 primary THA was performed by single senior expert surgeon. After excluding 40 THA with metal-on-polyethylene bearing and 17 THA with 32 mm ceramic head with cup size less than 52 mm, 155 primary ceramic-on-ceramic THAs with 4th generation 36 mm ceramic head were performed for 140 patients. Excluding THAs with less than 2 years of follow-up, 133 ceramic-on-ceramic THAs with 36 mm head for 129 patients were included in the present study. During the same period, no 28 mm ceramic head was implanted. For comparison, ceramic-on-ceramic THA with 3rd generation 28 mm head was set as a historical control group. From 2004 to 2010, 405 primary ceramic-on-ceramic THAs with 28 mm head were performed. Based on age, gender, and etiology of THA, a propensity score was calculated, and a one-to-one matching was performed. Eventually, 133 ceramic-on-ceramic THA with 3rd generation 28 mm head in 128 patients were identified. After obtaining approval from the Institutional Review Board, medical records and radiological data of patients in both groups were retrospectively evaluated by one of the authors who did not participate in the primary THA. All procedures followed were in accordance with the ethical standards of the responsible committee on human experimentation (institutional or regional) and with the Helsinki Declaration of 1975, as revised in 2000.

There were 83 men and 50 women in both groups. Preoperative features of both groups are shown in Table 1. Both groups showed no significant difference in preoperative demographic features. Before propensity score matching, both groups showed a significant difference in gender, height, and follow-up. After propensity score matching, both groups showed similar demographic feature without any significant difference except for follow-up period (4.2 years in the 36 mm group and 6.4 years in the 28 mm group, p < 0.001).

Table 1.

Preoperative demographic features of patients who underwent ceramic-on-ceramic total hip arthroplasties with 4th generation 36 mm head (36 mm group) or 3rd generation 28 mm head (28 mm group) before and after propensity score matching (PSM)

Demographics	36 mm group	28 mm group before PSM	p value	28 mm group after PSM	p value
Number of hips	133	405		133
Number of patients	129	380		128
Gender (male:female)	83:50	211:194	0.04*	83:50	1.0
Age (years)	55.5 ± 11.3	56.5 ± 13.5	0.70	55.4 ± 11.3	0.93
Etiology (%)			0.23		0.58
Osteonecrosis	75 (56.4%)	233 (57.5%)		81 (60.9%)
Osteoarthritis	16 (12.0%)	24 (5.9%)		13 (9.8%)
Hip dysplasia	14 (10.5%)	58 (14.3%)		17 (4.2%)
Hip fracture	13 (9.8%)	58 (14.3%)		15 (11.2%)
LCP sequalae	15 (11.2%)	10 (2.5%)		7 (5.3%)
Rheumatoid arthritis	6 (4.5%)	17 (4.2%)		4 (3.0%)
Ankylosing spondylitis	3 (2.3%)	5 (1.2%)		2 (1.5%)
Height (cm)	162.6 ± 8.3	159.4 ± 9.8	0.03*	162.1 ± 8.0	0.94
Weight (kg)	62.7 ± 9.3	60.6 ± 11.4	0.09	62.5 ± 9.1	0.87
Body mass index	23.8 ± 3.8	23.4 ± 3.9	0.94	23.8 ± 3.5	0.91
Follow-up (years)	4.2 ± 1.9	6.7 ± 4.0	< 0.001*	6.4 ± 3.6	< 0.001

PSM propensity score matching, LCP Legg–Calve–Perthes disease

*p value < 0.05

In both groups, THAs were performed with the same procedure by a single senior expert surgeon using direct lateral-transgluteal Hardinge approach in the lateral position [19]. After approach and acetabular preparation, the cementless cup was inserted by press-fit maneuver, and a liner was inserted. During insertion of the liner for Pinnacle cup, the ceramic liner was inserted with the gripper (Fig. 1). During liner insertion, the position of the liner was repeatedly checked to prevent malposition. Then, after femoral preparation, the cementless femoral stem was implanted, and the ceramic head was inserted. After reduction, leg length and ROM were evaluated, and the wound was closed by layer with care to repair abductor.

Fig. 1.

Insertion of the ceramic liner with the gripper. a Ceramic liner is placed in the gripper. b The gripper is placed at the margin of the cup and the liner is inserted by pressing the gripper. c The liner is fixed by gentle hammering. d The liner is placed correctly

Postoperatively, abduction pillow was applied during a hospital stay. Flexion of more than 90° or adduction across the midline was prohibited until 6 weeks after the operation. Weight-bearing was permitted within 3 days after the operation. Partial weight bearing was recommended with two crutches until postoperative 6 weeks. After 6 weeks, full weight bearing with one crutch or cane on opposite site was permitted, and daily activity without support was allowed after postoperative 3 months. Patients visited the outpatient clinic at postoperative 6 weeks, 3 months, 6 months, and 1 year. After postoperative 1 year, patients were followed-up annually.

For the 36 mm group, Trilock-BPS stems (DePuy, Warsaw, IN, USA) were inserted for 50 cases, while Summit stems (DePuy, USA) were inserted for 83 cases. Fourth-generation Biolox Delta (CeramTec AG, Plochingen, Germany) ceramic head and liner were inserted as bearing surface for all cases with Pinnacle Cup (DePuy, USA). For the 28 mm group, Summit stem and Duraloc option Cup (DePuy, USA) were inserted with 3rd generation Biolox Forte (CeramTec AG, Germany) ceramic head and liner in all cases. Features of the implant in both groups are shown in Table 2. The size of acetabular shell in the 36 mm group was slightly larger (p = 0.031) than that in the 28 mm group.

Table 2.

Features of implants of ceramic-on-ceramic total hip arthroplasties with 3rd generation 28 mm head or 4th generation 36 mm head

	28 mm group	36 mm group	p value
Stem (number)	Summit (133)	Summit (83), Trilock-BPS (50)
Cup	Duraloc option	Pinnacle
Ceramic bearing	Biolox Forte	Biolox Delta
Cup size	53.6 ± 2.9	54.9 ± 2.2	0.03*
Neck length			0.98
Short	20	19
Medium	76	76
Long	37	38

*p value < 0.05

For clinical evaluation, Harris Hip Score (HHS) was evaluated preoperatively. During the hospital stay, in cases with the suspicious sign of delirium such as confusion, loss of orientation, or behavioral change, consultation was made to a psychiatrist and presence of delirium was evaluated. In the outpatient clinic, clinical evaluation was performed with HHS and patients were asked about the presence of inguinal or thigh pain. Presence of noise, snapping, and squeaking was also evaluated. The occurrence of other complication was recorded.

For radiologic evaluation, cup inclination was measured in AP radiograph. Anteversion of the cup was evaluated in the trans-lateral radiograph by the method suggested by Woo and Morrey [20]. The cup placed out of Lewinnek’s safe zone was considered as an outlier [21]. The presence of osteolysis and loosening was evaluated with serial X-ray [22–24].

Statistical analysis was performed using SPSS 20.0 (IBM, New York, NY, USA). One-to-one matching between THAs with 4th generation 36 mm ceramic head and THAs with 3rd generation 28 mm ceramic head was performed by propensity score matching as a better alternative in studies with multiple baseline characteristics [25]. The propensity score was calculated with a multiple logistic regression model with variables including patient’s age, gender, and etiology of THA using SPSS 20.0 for both groups (133 THAs with 4th generation 36 mm ceramic head and 405 THAs with 3rd generation 28 mm ceramic head). Based on the calculated propensity score, one-to-one matching was performed with SPSS macro-program. To match 133 THAs with 36 mm head, 133 THAs were identified from 405 THAs with 28 mm head [26]. Paired t test was performed to compare preoperative and postoperative HHS. Student’s t test was performed to compare numeric variables between the two groups. For non-numeric variables, Pearson’s chi-squared test and Fisher’s exact t test were performed. p value of less than 0.05 was regarded as statistically significant.

Results

Results of ceramic-on-ceramic THA with 3rd generation 28 mm ceramic head and 4th generation 36 mm ceramic head are shown in Table 3. Harris Hip Scores were increased significantly (p < 0.001) in both groups after THA. During the hospital stay, nine patients in the 28 mm group and eight patients in the 36 mm group showed signs of delirium and diagnosed with delirium. During follow-up at the outpatient clinic, four patients in the 36 mm group and three patients in the 28 mm group complained about noise. However, no squeaking or snapping was reproducible at the outpatient clinic.

Table 3.

Results of ceramic–ceramic total hip arthroplasties with 3rd generation 28 mm heads or 4th generation 36 mm head

	28 mm group	36 mm group	p value
Harris Hip Score (points)
Preoperative	46.7 ± 7.8	46.4 ± 8.1	0.89
Postoperative	93.6 ± 4.2	92.1 ± 3.6	0.91
Cup position
Mean inclination angle	41.9° ± 5.4°	42.3° ± 5.3°	0.91
Inclination outlier	9	10	0.81
Mean anteversion angle	22.2° ± 11.8°	24.2° ± 12.0°	0.86
Anteversion outlier	19	18	0.86
Complication
Postoperative delirium	9	8	0.80
Dislocation	6	0	0.03*
Periprosthetic joint infection	2	0	0.50
Noise	4	3	1.0
Snapping sound	3	2	1.0
Squeaking	1	1	1.0
Inguinal pain	2	3	1.0

*p value < 0.05

Radiologically, cup position and number of outlier showed no difference in both groups. No osteolysis or loosening was observed in the 36 mm group. In the 28 mm group, no osteolysis or loosening was observed except for one acetabular with the sign of progressive osteolysis around cup and loosening. Periprosthetic joint infection (PJI) with septic loosening was diagnosed with elevated level of serum white blood cell count and C-reactive protein (CRP) in the case. Another one THA showed sign of PJI with fistula formation without the radiologic sign of osteolysis or loosening. These two hips were treated with implant removal and staged revision.

As for complication, no dislocation occurred in the 36 mm group. However, six dislocations occurred (four male and two female patients with mean age of 61.2 years) in the 28 mm group (Table 4). All dislocations occurred within 5 weeks after the operation (mean, 21.8 days) during excessive ROM. Four out of 6 patients with dislocation showed signs of delirium at hospital stay. After treatment, no recurrent dislocation occurred. PJI occurred in two hips in the 28 mm group, and one THA in each group showed sign of superficial wound infection and treated with debridement with implant retention. Otherwise, no ceramic bearing fracture or periprosthetic fracture occurred during follow-up.

Table 4.

Features of patients with dislocation after total hip arthroplasty with 28 mm head

Number	Gender	Age	Height	Weight	BMI	Postoperative delirium	Cup inclination	Cup anteversion	Stem anteversion	POD at dislocation	Activity before dislocation	Direction of dislocation	Treatment
1	Male	59	172	60	19.9	Yes	29.9	6.2	33.2	27	High flexion	Posterior	Cup revision
2	Female	60	160	51	23.8	Yes	27.8	11.1	14.6	16	High flexion	Posterior	Closed reduction
3	Female	64	160	61	19.0	No	46	34.8	10.5	22	Squatting	Anterior	Cup revision
4	Male	62	170	55	24.2	Yes	39	32.8	14.3	20	Squatting	Anterior	Closed reduction
5	Male	57	160	62	26.6	No	37.2	24.7	6.8	32	Squatting	Posterior	Abductor repair
6	Male	65	155	64	22.9	Yes	48.7	16.9	25.9	14	Squatting	Posterior	Closed reduction

BMI body mass index, POD postoperative day

Discussion

In the previous studies which compared the result of the 3rd generation ceramic-on-ceramic THA with 28 mm head to that with the 32 mm head, THA with 32 mm head showed comparable functional score and complication rate including dislocation and ceramic liner fracture [27–29]. Recently, the 4th generation ceramic bearing has been introduced and the larger sized head has been available for THA. The problem with the large-sized ceramic head is not established. The present study showed that ceramic-on-ceramic THAs with 4th generation 36 mm ceramic head had favorable short-term outcomes. Compared to THAs with 3rd generation 28 mm ceramic head, postoperative dislocation rate was decreased significantly in THAs with 36 mm ceramic head without increasing the rate of squeaking or inguinal pain. No ceramic bearing fracture was observed.

The 36 mm head significantly reduced the rate of dislocation compared to the 28 mm head in the present study. Dislocation can occur with multi-factorial etiology [1]. The surgical approach is one of the most critical risk factors for dislocation [1]. In the present study, the direct lateral approach was performed, and the hip joint was dislocated anteriorly during operation in all cases. The present study showed rates of dislocation (overall 2.2%) similar to those of previous studies on THA using the direct lateral approach [30, 31]. However, the 28 mm group of the present study showed a relatively higher rate of dislocation. All dislocations occurred within 5 weeks after THA, and four dislocations occurred in six patients with delirium in the 28 mm group. Postoperative delirium might be a potential risk factor for dislocation after THA [32, 33]. Poor cooperation under delirious condition might result in unexpected excessive ROM and dislocation of the prosthetic joint during the early postoperative period before maturation of soft tissue. Hence, small prosthetic head size and delirious condition of patients might have contributed to the high dislocation rate in the 28 mm group of the present study. The 36 mm group showed no postoperative dislocation, although there was no difference in the rate of postoperative delirium between the 28 mm and the 36 mm groups. In the previous study about the postoperative ROM after ceramic-on-ceramic with different head sizes (28 mm, 32 mm, and 36 mm), THA with 36 mm head showed significant better postoperative-6-week ROM score than THA with 28 mm head [28]. Using the 36 mm head might have increased early postoperative ROM and jumping distance, thus preventing dislocation even under excessive ROM under delirious condition in the early postoperative period.

Squeaking is one of the most significant and unique complications of THA with the ceramic-on-ceramic bearing [13, 15]. Many studies have shown various rates of squeaking. Various factors have been suggested as risk factors for squeaking [13]. However, no factors except specific types of cup and stem have constantly been suggested as related factors [13]. In the present study, one patient in each group reported squeaking. However, no squeaking was reproducible in the clinic. The previous studies which compared the results of the 3rd generation ceramic-on-ceramic THA with 28 mm head to those with 32 mm head showed no significant difference in squeaking rate [27–29]. However, there were two studies which reported relatively high rates of squeaking with preassembled monobloc ceramic liner cup using the large ceramic head (diameter of more than 40 mm) [15, 34]. Increased torque force in bearing surface by large femoral head has been suggested as the reason for squeaking [15, 34]. In the present study, squeaking rates were not significantly higher than those with the conventional sized head. The increase of head size to 36 mm did not appear to increase the rate of squeaking, unlike the extremely large size of the ceramic head.

Ceramic fracture is one of the unique and severe complications of THA with the ceramic-on-ceramic bearing [12]. With 4th generation ceramic bearing, the rate of ceramic head fracture can be decreased remarkably, but the rate of liner fracture was not reduced as remarkably as that of head fracture [14]. Ceramic liner fracture is associated with a technical error during operation [14]. Mal-seating of the ceramic liner on the acetabular shell is a well-known risk factor for ceramic liner fracture [14]. Taper angle and morphology of the inner surface of the cup are known risk factors for mal-seating [14]. In the present study, gripper was used in all cases with 4th generation ceramic bearing, and the position of the liner was repeatedly checked to prevent mal-seating of ceramic liner. No ceramic liner fracture was observed in this study. Therefore, the careful surgical technique might be essential to prevent liner fracture in ceramic-on-ceramic THA.

In the current study, cup size was significantly larger in the 36 mm group. There is a limitation of use of 36 mm head in THA due to the limited size of cup. Though the minimal thickness of ceramic liner decreased with the introduction of Biolox Delta ceramic bearing, minimum 52 mm sized cup is required to use 36 mm head in THA [28]. In the 28 mm group of the current study, the proportion of female patients decreased and mean height of patients increased with propensity score matching. Moreover, though propensity score matching was performed, the cup size was significantly larger in 36 mm group than in 28 mm group in the current study. For Asian patients with short stature or female patients, implantation of 52 mm cup might be problematic due to small size of the acetabulum [28]. Implantation of larger sized cup more than suitable size might increase risk of complications. Intraoperative acetabular fracture during total hip arthroplasty is a very rare, but serious complication, and it might occur due to excessive over-reaming or implantation of oversized cup [35, 36]. Implantation of oversized cup might result in the anterior cup overhanging which might cause iliopsoas tendonitis [37]. The present study showed no difference in the postoperative complication-related increased cup size; however, further study is necessitated for evaluation of the results of THA with large cup size, especially in the Asian patient with the relatively small size of the pelvis. Careful preoperative templating is necessary to predict exact size of the cup in these patients. In case of small size of acetabular expected cup with high risk of postoperative dislocation, dual mobility cup could be a possible alternative option.

The present study has a few limitations. First, the number of patients was relatively small in this retrospective study. However, with propensity score matching, selection bias was minimized. Before propensity score matching, there was a significant difference in gender and height between two group, but there was no significant difference after propensity score matching. Second, THAs with 28 mm head and THAs with 36 mm head were not performed at the same period. However, one single surgeon performed all operations with the same procedure. The surgeon had more than 15 years of experience in THA. He had performed more than 1500 cases of THA when he started to perform THA with 3rd generation 28 mm head. Also, the position of cup and stem showed no significant difference between the two groups Third, two different implants were used in the 36 mm THA group. Implant design is an important factor for instability [1]. However, both stems show similar design in proximal geometry including offset, neck length, and neck-shaft angle. Hence, the impact of implant design on dislocation was minimized in this study. Fourth, the follow-up period of both groups showed a significant difference in the current study. In this study, all dislocation in the 28 mm group occurred in the early postoperative period, and no dislocation occurred in the 36 mm group until the short-term follow-up. However, there is a concern about late dislocation after THA. In the previous study by Hernigou et al. THA with ceramic-on-ceramic bearing showed lower late dislocation compared to THA with polyethylene liner [38]. Another study showed lower rate dislocation rate after THA with 36 mm ceramic head compared to that with 36 mm metal head [39]. Further study might be necessitated to confirm the lower late dislocation of ceramic-on-ceramic THA with 36 mm head compared to that with 28 mm head. Fifth, the two groups showed a significant difference in the length of follow-up and follow-up period was relatively short. Hence, it is difficult to compare the long-term complications which might increase in number with follow-up, between two group. As for dislocation, however, all dislocations occurred within 6 weeks after operation before maturation of soft tissue in the 28 mm group. No dislocation occurred after 6 weeks with the direct lateral approach. Also, there was no recurrent dislocation after the treatment. Hence, dislocation as a short-term complication after THA might be reduced with 36 mm head compared to 28 mm head. However, longer follow-up is needed to support the findings of the present study. Finally, HHS used in this study for assessment of clinical results is not pure patient reported outcome measurement (PROM) tool. HHS combines patient and clinician reported information and there is a potential risk of observer bias [40]. Also, HHS has a ceiling effect which could limit its validity [41]. However, HHS is the most common PROM tool in the THA studies in the major orthopedic journal [42]. Also, it has proven its usefulness in the short-term studies [41].

Conclusion

The 4th generation ceramic-on-ceramic THA with 36 mm head showed favorable short-term clinical and radiological results. Early postoperative dislocation in the THA group with 36 mm head was reduced significantly without increasing the rate of inguinal pain or squeaking compared to that in the THA group with 28 mm head. Therefore, THA using 4th generation 36 mm head might be a reliable treatment option with less concern about dislocation, inguinal pain, squeaking, or ceramic bearing fracture for patients with expected cup size more than 52 mm compared to THA with 3rd generation 28 mm head.

Author contributions

LSJ: Data collection, Statistics, Manuscript writing; YKS: Study design, Manuscript writing.

Funding

There is no funding source for this article.

Compliance with Ethical Standards

Conflict of interest

Authors have nothing to disclose.

Ethical standard statement

This article does not contain any studies with human or animal subjects performed by the any of the authors.

Informed consent

For this type of study informed consent is not required.