Comparative outcomes of single condylar replacement and total knee arthroplasty in elderly patients with knee osteoarthritis: A controlled clinical study

Abstract

Introduction

Osteoarthritis is a frequent degenerative joint disease, affecting older individuals in particular. When non-surgical treatment options are no longer effective or warranted, surgical options include single condylar replacement (SCR) or total knee arthroplasty (TKA). The optimal surgical approach for elderly patients remains a subject of debate, particularly with respect to short-term recovery and functional outcomes.

Materials and Methods

82 elderly patients with knee osteoarthritis treated between March 2022 and May 2023 were included in this controlled clinical study. Patients were allocated to the SCR group (n = 41) or TKA group (n = 41) based on clinical indication and patient preference in this non-randomized controlled study. Perioperative parameters, early postoperative inflammatory markers (C-reactive protein and interleukin-6), pain severity (visual analogue scale), knee function (Knee Society Score and Hospital for Special Surgery score), knee mobility, and short-term postoperative complications were evaluated.

Results

SCR was associated with shorter operative time and improved short-term functional outcomes compared with TKA. Early postoperative CRP, IL-6, and VAS scores were lower in the SCR group (p < 0.05). At 6 months, knee mobility and functional scores (KSS, HSS, and AIMS2-SF) were higher in the SCR group (p < 0.05). Differences in complication rates were observed, but should be interpreted cautiously given the short follow-up.

Conclusion

SCR was associated with improved short-term perioperative recovery and functional outcomes in selected elderly patients. Given the non-randomized design and short follow-up, these findings reflect association rather than superiority. Long-term outcomes and implant survival require confirmation in larger studies with extended follow-up.

Introduction

At present, about 528 million people worldwide suffer from osteoarthritis, of which about 365 million suffer from knee osteoarthritis, and most of them occur in the elderly.^1,2 The risk of osteoarthritis in the elderly surpasses that in young adults, and its management presents greater challenges. Clinically, prioritizing the treatment of elderly patients is imperative, necessitating the selection of safe and efficacious treatment strategies. Knee osteoarthritis, characterized by chronic degeneration primarily in the medial compartment, often results in restricted joint mobility, persistent pain, decreased physical activity, and may contribute to the development of diabetes, obesity, and cardiovascular disease, thereby amplifying the life and economic burden on patients.^3,4 Conservative therapy is the main treatment of the disease, and surgical treatment will be considered only for those who are unresponsive. Currently, total knee arthroplasty and single condylar replacement are the primary surgical procedures for this condition, which can effectively correct knee varus and relieve pain. Total knee arthroplasty primarily involves osteotomy and prosthetic implantation to optimize limb alignment, while osteophyte removal effectively alleviates knee joint pain and impedes disease progression. ³ This approach helps preserve bone mass and the integrity of the anterior and posterior cruciate ligaments, thereby maintaining the joint’s anatomical structure and preserving its biomechanical functionality. ⁵ In recent years, it has been found that total knee arthroplasty is more likely to lose more normal bone and soft tissue, resulting in loss of proprioception, while single condylar replacement is more likely to increase the stress on the tibial parts and enlarge the wear of the prosthesis.^6,7

Given that elderly patients often have reduced physiological reserve, multiple comorbidities, and diminished tissue reparative capacity, the selection of surgical strategies remains a subject of ongoing clinical debate.

Although numerous studies have evaluated the clinical outcomes of SCR and TKA in elderly patients with knee osteoarthritis, considerable heterogeneity in study design, outcome measures, and follow-up duration has led to inconsistent conclusions. Importantly, many studies emphasize long-term implant survival, while fewer investigations have focused specifically on perioperative trauma, early inflammatory response, and short-term functional recovery in elderly patients ⁸ .

The present study was therefore designed to focus on short-term postoperative outcomes, particularly perioperative recovery and early functional improvement following SCR and TKA. Serum C-reactive protein (CRP) and interleukin-6 (IL-6) were included as biomarkers reflecting surgical invasiveness and early postoperative inflammatory response. These markers were not intended to assess infection risk or predict long-term implant survival, but rather to provide insight into the magnitude of surgical trauma associated with each procedure.

Based on this background, a controlled clinical study was conducted at XX Hospital to compare short-term perioperative outcomes, early inflammatory response, pain relief, functional recovery, and complication profiles between SCR and TKA in elderly patients with knee osteoarthritis. The findings aim to provide clinically relevant evidence to support surgical decision-making in this specific patient population.

There are no randomized comparative data on older patients, and evidence of short-term recovery is limited. Therefore, the goal of this controlled clinical study was to examine the associations between SCR and TKA and perioperative recovery and early functional outcomes, rather than to determine procedural superiority.

Materials and methods

Study design and participants

The purpose of the investigation was to develop a clinical study with an appropriately controlled design. A sample of 82 previously described elderly patients with knee osteoarthritis who were treated at XX Hospital during the time period of March 2022 through May 2023 was selected for the study. The patients were separated into two treatment groups based upon patient preference and clinical indication, resulting in 41 patients receiving single condylar replacements (SCR) and 41 patients receiving total knee arthroplasty (TKA).

Patients were allocated based on clinical indication and patient preference. As this was a non-randomized study, selection bias cannot be excluded, and outcomes should be interpreted as associative rather than comparative superiority.

Because the current investigation did not use randomization, allocation concealment, or blinding, the factors outlined above were not incorporated into the analysis. The protocol of the current investigation was reviewed and approved by the Medical Ethics Committee of Zigong Hospital of Traditional Chinese Medicine (IRB approval number: XXXX). Written informed consent was obtained from all of the participants prior to enrollment.

The same surgical team performed all procedures in both groups, thereby ensuring consistency in surgical technique. The manufacturers of the implants and laboratory reagents had no role in the study design, data collection, data analysis, interpretation of results, or manuscript preparation. Comorbidities, ASA classification, and surgeon-related variability were not formally adjusted for.

Flowchart overview of the study design, including patient selection, group allocation, intervention procedures, and follow-up (Figure 1).

Figure 1.

Flowchart overview of the study design, including patient selection, group allocation, intervention procedures, and follow-up.

Sample size calculation

Calculation formula of sample size:

$n=2\times {\left[\frac{\left({\mathrm{u}}_{\alpha }+{\mathrm{u}}_{\beta }\right)\times \sigma }{\delta }\right]}^2$

• U α-the value of u that corresponds to level α

• U value that is equivalent to the error probability β of the uβ-II type

• δ-the variance between the two averages of the populations, δ = μ 1-μ 2

• σ-total standard deviation

The lookup table for statistics indicates that the critical value for a two-tailed test (α = 0.05) is 1.96, and for β = 0.1, the respective Z-value was 1.282. The American Hospital for Special Surgery Knee-Rating Scale (HSS) was chosen as an outcome measure based on literature reviews and previous studies [1]. With a reported mean difference δ = 3.44, group sizes n₁ = n₂ = 45, standard deviations S₁ = 5.23, S₂ = 6.32, and a pooled standard deviation σ ≈ 4.19, the final formative sample size per group was 37 cases. After accounting for a potential 10% attrition rate, approximately 41 patients were included in each group. The sample size calculation was performed for functional outcome assessment rather than for detecting differences in complication rates; therefore, analyses of complications were considered exploratory.

Inclusion and exclusion criteria

Patients were eligible for inclusion if they met established diagnostic criteria for knee osteoarthritis 9 and had imaging confirmation of isolated medial compartment involvement. Eligible patients were aged between 60 and 80 years and presented with knee varus deformity and flexion contracture not exceeding 15°. All included patients experienced persistent pain and functional limitation despite failure of conservative treatment, with radiographic evidence of joint degeneration. Additionally, intact knee ligament function was required, and written informed consent was obtained from all participants prior to enrolment.

Patients were excluded if they had bone tumors, bone Tuberculosis, rheumatoid arthritis, or other inflammatory joint diseases. Exclusion criteria also included severe hematologic disorders, limb dysfunction, previous knee surgery, a history of severe trauma or lower limb deformity, significant hepatic or renal impairment, or psychiatric disorders that could interfere with treatment compliance or follow-up.

Surgical procedures

Routine preoperative preparation was performed in both groups, and all patients were managed by the same surgical team.

In the SCR group, an 8–10 cm medial knee incision was made under anaesthesia. The medial meniscus was removed, hyperplastic synovium was cleared, and care was taken to preserve the anterior and posterior cruciate ligaments. Tibial plateau osteotomy was performed using an osteotomy guide, followed by posterior condylar osteotomy and grinding. Trial components were used to confirm appropriate flexion, extension, and alignment before implantation of the Oxford unicondylar prosthesis using bone cement.

In the TKA group, a 15–20 cm midline incision was made under epidural anaesthesia. Tibial and femoral osteotomies were performed using standard intramedullary guides. Trial components were assessed to ensure appropriate knee alignment and motion prior to definitive prosthesis implantation with bone cement.

Drainage tubes were removed 2–3 days postoperatively, and patients were encouraged to begin early mobilization and functional rehabilitation. All patients were followed for 6 months.

Outcome measures

Operative indices included postoperative drainage volume, intraoperative blood loss, operation time, time to straight leg elevation, and time to active knee flexion to 90°.

Serum C-reactive protein (CRP) and interleukin-6 (IL-6) levels were measured preoperatively and 24 h postoperatively to reflect perioperative surgical trauma and early inflammatory response rather than infection or long-term outcomes.

Pain severity was assessed using the Visual Analogue Scale (VAS). ⁹ Knee function was evaluated using the Knee Society Score (KSS) ¹⁰ and the Hospital for Special Surgery (HSS) score. ¹¹ Quality of life was assessed using the Short-Form Arthritis Impact Measurement Scales 2 (AIMS2-SF). ¹² Knee joint mobility was measured using a standard goniometer.

Postoperative complications, including wound infection, recurrence of knee varus, prosthesis loosening, and deep vein thrombosis, were documented. Given the limited sample size and short follow-up duration, complication outcomes were analyzed descriptively and considered exploratory. Complication outcomes were descriptive and hypothesis-generating only.

Statistical analysis

Statistical analyses were performed using SPSS version 24.0. Continuous variables were expressed as mean ± standard deviation. Intergroup comparisons were conducted using independent-sample t-tests, and intragroup comparisons were performed using paired-sample t-tests. Categorical variables were compared using the χ² test.

Effect sizes for primary functional outcomes were reported as mean differences with 95% confidence intervals.

No multivariate analysis was performed due to the limited sample size and insufficient statistical power to adjust for multiple confounding variables. No propensity matching or multivariable adjustment was performed due to the limited sample size.

A p value <0.05 was considered statistically significant.

Results

Comparison of the two groups of baseline data

There wasn’t a noticeable variation in age, sex, body mass index (BMI), course of disease, lesion site, Kellgren-Lawrence classification, and years of education involving the single condyle replacement group and the total knee replacement group (P > 0.05), as shown in Table 1. These findings indicate comparability at baseline between the two groups with respect to the variables.

Table 1.

Comparison of two sets of baseline data.

Project	Single condylar replacement group (n = 41)	Total knee arthroplasty group (n = 41)	t/χ 2	P
Age (years, $\overline{x}\pm s$ )	67.82 ± 3.55	68.03 ± 3.61	0.265	0.791
Gender [n (%)]
Male	18 (43.90)	20 (48.78)	0.196	0.658
Female	23 (56.10)	21 (51.22)
Course of disease (month, $\overline{x}\pm s$ )	9.42 ± 1.13	9.37 ± 1.11	0.202	0.840
BMI index (kg/m2, $\overline{x}\pm s$ )	23.14 ± 0.77	23.09 ± 0.75	0.297	0.766
Lesion site [n (%)]
Left side	19 (46.34)	22 (53.66)	0.198	0.656
Right side	17 (41.46)	24 (58.54)
Kellgren-Lawrence grading [n (%)]
II	22 (53.66)	24 (58.54)	0.212	0.899
III	17 (41.46)	15 (36.59)
IV	2 (4.88)	2 (4.88)
Years of education	9.55 ± 2.10	9.59 ± 2.15	0.085	0.932

Comparison of operative indexes involving the two groupings

As illustrated in Figure 2 and Table 2, the single condyle replacement group had significantly shorter operation, straight leg elevation, active flexion to 90°, hospitalization, postoperative drainage, and intraoperative blood loss times than the total knee replacement group (p < 0.05). These results reflect observed differences in perioperative and early postoperative recovery parameters between the two surgical approaches.

Figure 2.

Comparison of surgical indexes involving the two groupings (P < 0.05). Bar graphs illustrating key operative outcomes such as operation time, intraoperative blood loss, drainage volume, and recovery time between the SCR and TKA groups.

Table 2.

Comparison of surgical indexes involving the two groupings ( $\overline{x}\pm s$ ).

Group	n	Operation time (min)	Intraoperative bleeding volume (mL)	Postoperative drainage (mL)	Straight leg raising time(d)	Active flexion to 90 °time (d)	Hospitalization time(d)
Single condylar replacement group	41	66.47 ± 7.98	214.27 ± 25.68	101.68 ± 11.64	2.77 ± 0.33	3.23 ± 0.39	8.67 ± 1.04
Total knee arthroplasty group	41	87.18 ± 8.46	351.46 ± 32.12	234.33 ± 14.55	3.89 ± 0.38	6.64 ± 0.46	11.55 ± 1.17
t		11.402	21.361	45.817	14.249	36.205	11.780
P		<0.001	<0.001	<0.001	<0.001	<0.001	<0.001

Comparison of serum IL-6 and CRP levels

There wasn’t a noticeable variation in serum IL-6 and CRP levels between the two groupings before operation (p > 0.05). Table 3 and Figure 3 demonstrate that blood levels of IL-6 and CRP rose in both groups 24 h post-op, with the single condyle replacement group having lower levels than the complete knee replacement group (p < 0.05). At this time point, the single condylar replacement group exhibited lower postoperative IL-6 and CRP levels than the total knee arthroplasty group (p < 0.05), representing an observed difference in early inflammatory response.

Table 3.

Comparison of serum IL-6 and CRP involving the two groupings ( $\overline{x}\pm s$ ).

Group	n	IL-6 (pg/mL)		CRP (mg/L)
		Before operation	After operation 24h	Before operation	After operation 24 h
Single condylar replacement group	41	13.07 ± 1.57	42.30 ± 5.08①	7.05 ± 0.85	13.11 ± 1.57①
Total knee arthroplasty group	41	13.11 ± 1.58	62.27 ± 7.47①	7.09 ± 0.86	19.04 ± 1.88①
t		0.114	14.154	0.211	15.502
P		0.908	<0.001	0.832	<0.001

Note. Compared with before treatment, ^①p < 0.05.

Figure 3.

Comparison of serum CRP and IL-6 involving the two groupings (ns p > 0.05, p < 0.05). Graphical presentation of preoperative and 24-h postoperative serum CRP and IL-6 levels to assess inflammatory response in both groups.

VAS, KSS, HSS, and AIMS2-SF were compared between the two groupings

No statistically significant differences were found between the two groups in VAS, KSS, HSS, or AIMS2-SF preoperatively (P > 0.05). Both groups had lower VAS postoperatively and higher KSS, HSS, and AIMS2-SF at 6 months postoperatively. The single-condyle replacement group had lower VAS and higher KSS, HSS, and AIMS2-SF than the total knee arthroplasty group at the 6-month follow-up (p < 0.05). Between-group differences in the primary functional outcome measures were reported as means and corresponding 95% confidence intervals in Figure 4 and Table 4. Although statistically significant differences were observed, the magnitude of improvement should be interpreted in the context of the minimal clinically important difference (MCID), which was not formally assessed in this study.

Figure 4.

Comparison of VAS, KSS, HSS, and AIMS2-SF involving the two groupings (ns p > 0.05, p < 0.05). Line or bar graphs comparing pain scores (VAS), functional scores (KSS and HSS), and quality of life scores (AIMS2-SF) before and after surgery in both groups.

Table 4.

Comparison of VAS, KSS, HSS and AIMS2-SF involving the two groupings (points, $\overline{x}\pm s$ ).

Group	n	VAS Scoring		KSS Scoring		HSS Scoring		AIMS2-SF Scoring
		Before operation	After operation	Before operation	After operation	Before operation	After operation	Before operation	After operation
Single condylar replacement group	41	7.03 ± 0.84	1.82 ± 0.22①	51.44 ± 6.17	81.25 ± 9.75①	53.52 ± 6.42	80.21 ± 9.63①	60.26 ± 7.23	79.22 ± 9.51①
Total knee arthroplasty group	41	7.07 ± 0.86	3.27 ± 0.39①	51.52 ± 6.18	65.22 ± 7.82①	52.45 ± 6.29	72.56 ± 8.71①	60.31 ± 7.24	92.37 ± 11.08①
T		0.213	20.734	0.058	8.212	0.762	3.772	0.031	5.766
P		0.831	<0.001	0.953	<0.001	0.448	<0.001	0.975	<0.001

Note. Compared with before treatment, ^①p < 0.05.

These results pertain to short-term functional and pain outcomes, not to long-term benefits.

Comparison of the range of motion of the knee joint between the two groups

There were no significant differences between the two groups in preoperative maximum knee flexion angle, femorotibial angle, or overall knee range of motion (p > 0.05). Postoperatively, all assessed range-of-motion parameters improved in both groups. At 6 months, higher postoperative values were observed in the single condylar replacement group compared with the total knee arthroplasty group (p < 0.05), as shown in Table 5 and Figure 5. These results reflect observed short-term improvements in knee mobility.

Table 5.

Comparison of range of motion of knee joints involving the two groupings (°, $\overline{x}\pm s$ ).

Group	n	Maximum knee flexion angle		Angle of femur and tibia		Range of motion of knee joint
		Before operation	After operation	Before operation	After operation	Before operation	After operation
Single condylar replacement group	41	91.55 ± 7.98	130.53 ± 12.66①	164.26 ± 9.71	183.25 ± 13.99①	83.22 ± 6.44	103.54 ± 9.51①
Total knee arthroplasty group	41	91.61 ± 8.02	114.67 ± 10.76①	164.31 ± 9.73	176.63 ± 13.74①	83.27 ± 6.46	94.36 ± 9.24①
T		0.033	6.112	0.023	2.161	0.035	4.433
P		0.972	<0.001	0.981	0.033	0.972	<0.001

Note. Compared with before treatment, ^① p < 0.05.

Figure 5.

Comparison of knee joint mobility involving the two groupings (ns p > 0.05, p < 0.05). Illustration of changes in knee flexion angle, femoral-tibial angle, and range of motion pre- and post-operatively for each group.

Comparison of complications involving the two groupings

There was no recurrence of knee varus, prosthesis loosening, or deep vein thrombosis in the single condylar replacement group, but there was no recurrence of knee varus or prosthesis loosening in the total knee arthroplasty group; wound infection occurred in 3 cases, and deep vein thrombosis in 3 cases. There was a notable difference in the complication rate between the two groupings (p < 0.05; Table 6).

Table 6.

Comparison of complications involving the two groupings [n (%)].

Group	n	Wound infection	Recurrence of knee varus	Prosthesis loosening	Deep venous thrombosis	Total incidence rate
Single condylar replacement group	41	1 (2.44)	0 (0.00)	0 (0.00)	0 (0.00)	1 (2.44)
Total knee arthroplasty group	41	3 (7.32)	0 (0.00)	0 (0.00)	3 (7.32)	6 (14.63)
χ 2						3.905
P						0.048

Given the limited sample size and short follow-up duration, these findings on complications are exploratory and hypothesis-generating and should be interpreted with caution. No conclusions regarding implant longevity or long-term prosthesis survival can be drawn from these results. Given limited power and short follow-up, complication comparisons are exploratory.

Discussion

Knee osteoarthritis is a common orthopedic condition among older adults. Knee osteoarthritis is extremely harmful, which can lead to adverse consequences such as lower limb displacement and joint varus. The physical quality of elderly patients is not as good as that of young and middle-aged patients. If not treated in time, the quality of daily life will be seriously affected, and the harm caused by the disease is often more than that of young patients. ¹³ Elderly patients frequently present with reduced physiological reserve and multiple comorbidities. In this context, perioperative safety and short-term functional recovery are critical considerations when selecting surgical interventions for older patients.

Because treatment allocation was based on clinical indication and patient preference, selection bias cannot be excluded. Therefore, observed differences represent associations rather than evidence of procedural superiority.

For knee osteoarthritis, total knee arthroplasty is widely regarded as the primary treatment option, and its clinical effectiveness has been confirmed by long-term clinical practice across various etiologies of arthritis.^14–16 Total knee arthroplasty remains the gold standard for patients with advanced or multicompartmental knee osteoarthritis. However, it is also recognized that TKA may be associated with greater surgical trauma and perioperative burden, particularly in elderly patients, prompting consideration of alternative surgical strategies for carefully selected cases.

Single condylar replacement (SCR) has been proposed as a less invasive surgical option for patients with isolated compartment disease and preserved ligament function. Previous studies have shown that both TKA and SCR can effectively treat knee osteoarthritis when appropriately indicated.^17–19 However, comparative evidence focusing specifically on short-term outcomes in elderly populations remains limited, which formed the rationale for the present study.

The results of the present investigation demonstrated that the SCR group had shorter operative time, lower intraoperative blood loss, lower postoperative drainage volume, shorter time to functional mobilization, and shorter hospital stay than the TKA group. These findings reflect observed differences in perioperative invasiveness and early postoperative recovery rather than long-term surgical superiority. The limited surgical exposure associated with SCR, which preserves uninvolved compartments and surrounding structures, may contribute to these short-term advantages.^20–22

CRP and IL-6 were included in this study to reflect the early postoperative inflammatory response associated with surgical invasiveness, rather than to predict infection or long-term outcomes. Both biomarkers increased postoperatively in both groups, which is consistent with expected surgical stress responses. Lower postoperative CRP and IL-6 levels observed in the SCR group likely reflect reduced tissue trauma and operative extent compared with TKA, which involves more extensive bone resection and soft-tissue manipulation. ²³ These findings should not be interpreted as indicators of infection or prognostic biomarkers.

Functional outcomes assessed at 6 months demonstrated improvements in pain, knee function, range of motion, and quality of life in both groups. At the 6-month follow-up, SCR was associated with better short-term pain relief and functional scores in this selected patient population. These findings do not contradict the existing literature supporting TKA as the preferred treatment for more advanced disease; rather, they may reflect potential short-term functional advantages in carefully selected elderly patients with isolated compartment disease and lower functional demands.

Although statistically significant differences were observed in pain and functional scores, clinical relevance should be interpreted cautiously, as minimal clinically important differences were not formally evaluated.

With regard to safety, differences in postoperative complication rates were observed; however, these findings should be interpreted cautiously. Given the limited sample size and short follow-up duration, complication outcomes in this study are exploratory and hypothesis-generating. No conclusions regarding implant survival, prosthesis longevity, or long-term complication risk can be drawn.

Variability in lesion characteristics and patient-specific surgical indications may have influenced outcomes. Subgroup analyzes were not feasible due to sample size; however, SCR-related findings likely depend on strict patient selection, including isolated compartment disease and intact ligaments.

Several limitations of this study should be acknowledged. The 6-month follow-up limits assessment of implant durability, revision rates, and long-term functional trajectories.

Several limitations of this study should be acknowledged. The follow-up duration was limited to 6 months, which precludes assessment of implant survival and long-term outcomes. Additionally, the sample size was modest and not powered to analyze complications, and confounding factors were not formally adjusted for. Future multicenter studies with larger cohorts and longer follow-up are needed to validate these findings.

Conclusion

This non-randomized controlled study indicates that SCR provides better short-term perioperative recovery and functional outcomes than TKA in carefully selected elderly patients. The data address only short-term associations and do not imply that SCR is superior to TKA in procedural terms. Long-term implant survival and durability cannot be evaluated until further randomized studies with longer follow-up have been conducted to confirm these results.