Uncemented slotted stem versus short stem for distal femoral endoprosthetic reconstruction in pediatric bone tumor patients: a retrospective analysis of prosthetic performance and functional outcomes

Abstract

Background

Uncemented endoprosthetic reconstruction is commonly used in pediatric patients after distal femoral tumour resection. However, conventional short stems may be associated with aseptic loosening, bone resorption, and end-of-stem pain, which may compromise long-term outcomes. This retrospective cohort study aimed to compare prosthetic loosening, bone resorption, and clinical outcomes between slotted stems and conventional short stems in pediatric patients undergoing uncemented distal femoral endoprosthetic reconstruction.

Methods

We performed a retrospective cohort study of pediatric patients who underwent implantation of an uncemented endoprosthesis with either a slotted stem or a conventional short stem between 2021 and 2023. Aseptic loosening and bone resorption were evaluated radiographically using radiolucent lines, stem axis displacement, and translucent bands. Clinical outcomes were assessed using the 1993 Musculoskeletal Tumor Society (MSTS-93) score and the rate of end-of-stem pain. Complications and endoprosthetic failures were also recorded.

Results

A total of 47 patients were included, including 24 in the slotted stem group and 23 in the control group. The median age was 9 years (range, 8–14) in the slotted stem group and 10 years (range, 7–14) in the control group. The median follow-up was 35 months (range, 24–49) in the slotted stem group and 36 months (range, 25–48) in the control group. No significant between-group difference was observed in the rate of radiographic aseptic loosening (4.17% vs. 8.70%, p = 0.609) or in bone resorption in Zones 1–4. However, the slotted stem group had less bone resorption in Zone 5 (p = 0.022). MSTS-93 scores were similar between groups (p = 0.574), whereas the slotted stem group had a lower rate of end-of-stem pain (p = 0.048).

Conclusions

In this retrospective cohort, the slotted stem showed comparable short-term outcomes to the conventional short stem, with less Zone 5 bone resorption and a lower rate of end-of-stem pain. Slotted stems are viable alternatives to short stems for distal femoral endoprosthetic reconstruction following tumour resection in pediatric patients.

Introduction

The metaphyseal regions of long bones, particularly around the knee joint, are predilection sites for bone tumors, accounting for approximately 30% to 40% of all bone neoplasms [1, 2]. Their diagnosis may occasionally be challenging because of overlapping clinical, imaging, and pathological features that require specialized expertise [3]. Among childhood malignancies, primary bone tumours such as osteosarcoma and Ewing sarcoma are important causes of cancer-related morbidity [4]. With advances in multimodal treatment and surgical techniques, limb-salvage surgery is now feasible in more than 90% of patients with malignant tumours of the lower limb [5, 6].

Since the 1970s, distal femoral endoprosthetic reconstruction has become a well-established and reliable limb-salvage option [7–9]. Distal femoral endoprosthetic reconstruction provides immediate fixation, allows early weight-bearing, facilitates functional recovery, and helps preserve limb function [10]. However, pediatric patients present unique reconstructive challenges because of their smaller bone size, shorter residual segments after tumour resection, and narrower medullary canals. These anatomical features may limit stem fixation length and reduce the area available for stable biological fixation, potentially compromising long-term implant stability.

Although pediatric and adult patients may achieve comparable functional improvement after endoprosthetic reconstruction of lower-extremity tumours [11], pediatric patients present distinct reconstructive challenges because of smaller bone dimensions, narrower medullary canals, and ongoing skeletal growth. Aseptic loosening remains one of the leading causes of endoprosthetic failure and is a major indication for revision surgery [12–14]. Many studies try to modify the shape [10], surface [15, 16], and length [17] of endoprosthetic stems, aiming to provide favorable initial stability while reducing the risk of prosthetic loosening. Slotted stems have been used in hip and knee arthroplasty and have been associated with reduced end-of-stem pain during postoperative activity [18, 19]. Moreover, biomechanical analyses have also suggested that slotted stems reduce stress-shielding, stress concentration, and fracture risk [20, 21].

However, clinical data on uncemented slotted stems in pediatric orthopaedic oncology remain limited. The technical challenges associated with limb reconstruction in skeletally immature patients further highlight the importance of tailored surgical strategies and implant design optimization [22]. Therefore, this study aimed to compare prosthetic loosening, bone resorption, complications, and functional outcomes between slotted stems and conventional short stems in pediatric patients undergoing uncemented distal femoral endoprosthetic reconstruction.

Materials and methods

The patient flow diagram is presented in Fig. 1. We conducted a retrospective analysis of the medical records of patients diagnosed with distal femoral tumours who had undergone uncemented endoprosthetic reconstruction with slotted stem (study group) and short stem(control group) following tumour resection from January 2021 to January 2023. This study was approved by the Biomedical Ethics Review Committee of the local hospital, and the study was reported in accordance with the Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) statement [23].

Fig. 1.

Flow diagram of patient enrollment and analysis

Study population

The criteria for inclusion into the study are as follows: (1) histologically confirmed malignant or intermediate distal femoral tumours treated with uncemented endoprosthetic reconstruction; (2) patients with malignant tumours who received neoadjuvant chemotherapy before surgery and showed a favourable imaging response; and (3) no pulmonary metastasis at initial diagnosis; (4) patients aged 7–14 years old at the time of surgery. The following are excluded: (1) metastatic tumours or non-oncological diseases; (2) tumour invasion of major neurovascular structures, poor imaging response to neoadjuvant chemotherapy, tumour progression of more than 20% before surgery, or newly detected distant metastasis before surgery; 3) receipt of both preoperative and postoperative radiotherapy; (4) incomplete follow-up data or follow-up of less than one year; and (5) participating in another trial that may affect the results of this trial.

Interventions

All endoprosthetic systems were manufactured by Beijing Chunlizhengda Medical Instruments Co., Ltd. (China). The articular surface was made of ultra-high-molecular-weight polyethylene (UHMWPE), and all other components were composed of titanium alloy (Ti6Al4V). The conventional short stem (control group) (Fig. 2) and the slotted stem (Fig. 3) were manufactured using forging technology, with an overall length of 110 mm and a taper of 0.1. The conventional short stem included a 10-mm non-press-fit tip. In the slotted stem, the slotted segment accounted for 40% to 60% of the total stem length. Stem diameters at the base ranged from 10 to 16 mm. In addition, the stem surface was coated with hydroxyapatite, with a total coating thickness of approximately 300 μm.

Fig. 2.

Photograph of an uncemented short stem coated with titanium particles and hydroxyapatite. A lateral B anteroposterior film of the short stem. C, D Simulation film of the short stem and implantation film

Fig. 3.

Photograph of an uncemented slotted stem coated with titanium particles and hydroxyapatite. A lateral B anteroposterior film of the slotted stem. C, D Simulation film of the slotted stem and implantation film

Consecutive eligible patients were included. Stem selection was based on anatomical considerations and surgeon preference. All procedures were performed by the same senior surgeon (C. Tu) and team. The osteotomy plane was carefully prepared to minimize component mismatch. After segmental tumour resection, a flexible reamer was used to enlarge the femoral medullary canal while preserving its native anterior curvature. To reduce bone loss and optimize primary stability, the canal was under-reamed by 0.5 mm relative to the stem diameter, with further adjustments made in 0.5-mm increments until stable press-fit fixation was achieved. In the slotted stem group, the reamer used for the slotted segment was 0.5 mm smaller than the slotted segment diameter to ensure adequate press-fit fixation. When a thin residual cortex or cortical fissure was identified, cerclage wire fixation was performed before stem implantation. The cerclage wires were removed if no cortical fracture occurred after stem insertion; otherwise, they were retained. After irrigation of the medullary canal and confirmation of satisfactory trial component positioning, the definitive stem was implanted. The knee prosthesis was then reduced, and stability was assessed during flexion-extension, rotation, and varus-valgus testing. A drainage tube was placed, and the wound was closed in layers.

Active knee range-of-motion exercises were initiated according to the patient’s postoperative condition, and partial weight-bearing was started on postoperative day 1–3, followed by gradual progression to full weight-bearing over the next 2 weeks based on wound healing, pain tolerance, and implant stability. This protocol was used to protect the bone-implant interface and soft-tissue reconstruction during the early postoperative phase.

Outcome assessments

The primary outcomes were bone resorption and aseptic loosening at the last follow-up. Bone resorption was assessed radiographically based on the presence of translucent bands around the uncemented stem. For this assessment, the prosthetic stem was divided into five zones, with Zone 1 located at the junction between the prosthetic body and stem and Zone 5 located at the distal end of the stem. In the slotted stem, the slotted portion was divided equally into three parts, and the remaining portion was divided into two parts. The stem in the control group was divided into five proportional zones using the same method (Fig. 4). Radiographic evaluation was performed on anteroposterior radiographs. Aseptic loosening was defined as stem migration in the absence of infection, specifically angular displacement of ≥ 1° or lateral/vertical displacement of ≥ 1 mm, as reported in our previous study [10]. Recognizable radiolucent lines (≥ 2.5 cm) between the stem and bone were recorded as radiographic signs of insufficient fixation and were interpreted together with stem migration findings.

Fig. 4.

Radiographs of the stem of the prosthesis(analysis zones)

The secondary outcomes included endoprosthetic failure requiring revision or implant removal, classified according to the Henderson classification [24], other postoperative complications, functional results measured by the Musculoskeletal Tumor Society (MSTS-93) score, and the rate of end-of-stem pain. The MSTS-93 is a validated and widely used functional assessment tool in musculoskeletal oncology [25]. Functional and radiographic outcomes were independently assessed by two investigators. In the event of disagreement, the images and records were re-evaluated jointly. If consensus could not be reached, a senior surgeon who was not involved in the initial assessment made the final determination.

Statistical analysis

Data analysis was performed using SPSS Statistics 19.0 for Windows (IBM Corporation), and graphs were generated using GraphPad Prism. No imputation was performed for missing data. Continuous variables were compared using the independent-samples t test when normally distributed and the Mann-Whitney U test when not normally distributed. Categorical variables were analyzed using the chi-square test or Fisher’s exact test, as appropriate. Because of the small sample size and limited number of outcome events, no multivariable analysis was performed. Statistical significance was defined as a two-sided p value < 0.05.

Results

Patient characteristics

A total of 118 patients were initially screened, of whom 50 met the eligibility criteria and were enrolled (Fig. 1). Three patients were lost to follow-up, resulting in a final follow-up rate of 94%. Therefore, 47 patients were included in the final analysis, including 24 in the slotted stem group and 23 in the control group. The median age was 9 years (range, 8–14) in the slotted group and 10 years (range, 7–14) in the control group. Baseline characteristics were comparable between the two groups (Table 1).

Table 1.

Baseline clinical characteristics of pediatric patients undergoing distal femoral endoprosthetic reconstruction

Characteristic	Slotted group (n = 24)	Control group (n = 23)	p value
Age, years, median (range)	9 (8 to 14)	10 (7 to 14)	0.167
Sex			0.891
Male, n (%)	11 (45.83)	11 (47.83)
Female, n (%)	13 (54.17)	12 (52.17)
Median follow-up periods, months (range)	35 (24 to 49)	36 (25 to 48)	0.341
Diagnosis, n (%)			0.609
Osteosarcoma	23 (95.83)	21 (91.30)
Others	1 (4.17)	2 (8.70)
Enneking stage, n (%)			0.666
IIA (Malignant)	2 (8.33)	3 (13.04)
IIB (Malignant)	22 (91.67)	20 (86.96)
TNM staging, n (%)			0.701
IIA	3 (12.50)	4 (17.39)
IIB	21 (87.50)	19 (82.61)
Resection length / total femoral length, n (%)			0.320
≤ 40%	2 (8.33)	4 (17.39)
40% to 60%	15 (62.50)	16 (69.57)
≥ 60%	7 (29.17)	3 (13.04)

Primary outcome

At the final follow-up, the rate of radiographic aseptic loosening did not differ significantly between the control group and the slotted stem group (8.70% vs. 4.17%, p = 0.609). Likewise, no significant between-group differences were observed in bone resorption in Zones 1–4 (Zone 1, p = 0.880; Zone 2, p = 0.920; Zone 3, p = 0.494; Zone 4, p = 0.245). However, bone resorption in Zone 5 was less frequent in the slotted stem group than in the control group (0/24 vs. 5/23, p = 0.022) (Table 2). Representative radiographic cases are shown in Figs. 5 and 6.

Table 2.

Radiographic, clinical, and oncologic outcomes after distal femoral endoprosthetic reconstruction

Characteristic	Slotted group (n = 24)	Control group (n = 23)	p value
Radiographic outcomes
Bone resorption, n (%)
Zone 1	8 (33.33)	8 (34.78)	0.880
Zone 2	6 (25.00)	6 (26.09)	0.920
Zone 3	4 (16.67)	6 (26.09)	0.494
Zone 4	2 (8.33)	5 (21.74)	0.245
Zone 5	0 (0)	5 (21.74)	0.022
Radiographic aseptic loosening at final follow-up, n (%)	1 (4.17)	2 (8.70)	0.609
Complication, n (%)
Wound dehiscence	1 (4.17)	1 (4.35)	0.999
Infection treated nonsurgically	1 (4.17)	2 (8.70)	0.609
Infection treated surgically	5 (20.83)	5 (21.74)	0.999
Endoprosthetic failures requiring revision or implant removal, n (%)*	3 (12.5)	5 (21.74)	0.461
Type I (soft-tissue failure)	1 (4.17)	1 (4.35)	0.999
Type II (aseptic loosening)	0 (0)	2 (8.70)	0.490
Type III (structural failure)	0 (0)	0 (0)	/
Type IV (infection)	1 (4.17)	1 (4.35)	0.999
Type V (tumour progression)	1 (4.17)	1 (4.35)	0.999
Functional and pain outcomes
MSTS-93 score, median (range)	81% (73% to 92%)	79% (71% to 90%)	0.574
End-of-Stem pain, n (%)	1 (4.17)	6 (26.09)	0.048
Oncologic outcomes
Metastasis, n (%)	2 (8.33)	1 (4.35)	0.999
Local recurrence, n (%)	1 (4.17)	1 (4.35)	0.999

*Classification of Henderson et al. MSTS-93, Musculoskeletal Tumour Society.

Fig. 5.

Anteroposterior and lateral X-ray in A, B Preoperative, C, D Postoperative, E, F 2-years postoperative of the patient with slotted stem. G, H Tomosynthesis-Shimadzu Metal Artifact Reduction Technology (T-SMART) images at 2 years postoperatively. Radiographs demonstrate bone resorption in Zones 1–4, with no radiographic evidence of aseptic loosening at the latest follow-up

Fig. 6.

Anteroposterior and lateral X-ray in A, B Preoperative, C, D Postoperative, E, F 2-years postoperative of the patient with short stem (Control). G, H Tomosynthesis-Shimadzu Metal Artifact Reduction Technology (T-SMART) images at 2 years postoperatively. Radiographs demonstrate bone resorption in Zones 1–5, with no radiographic evidence of aseptic loosening at the latest follow-up

Secondary outcome

Endoprosthetic failure requiring revision or implant removal occurred in 3 patients in the slotted stem group and 5 patients in the control group (12.50% vs. 21.74%, p = 0.461). According to the Henderson classification [24], the slotted stem group included one Type I failure, one Type IV failure, and one Type V failure, whereas the control group included one Type I failure, two Type II failures, one Type IV failure, and one Type V failure.

Other postoperative complications not requiring revision or implant removal are also summarized in Table 2. Wound dehiscence occurred in 2 patients in each group. Most infection-related events occurred within the first postoperative month and were associated with delayed wound healing, whereas only a minority occurred after 1 month. Infection treated non-surgically occurred in 1 patient in the slotted stem group and 2 patients in the control group. These patients presented with local erythema or swelling and elevated serum inflammatory markers, but without sinus tract formation, abscess, or fluid collection, and their symptoms improved after empirical antibiotic therapy. Surgically treated infection occurred in 5 patients in each group. These patients had sinus tract formation, abscess formation, fluid collection, or failure of antibiotic treatment and were managed with repeated debridement. If infection remained uncontrolled and involved the prosthesis, implant removal and antibiotic-loaded cement spacer implantation were performed, followed by staged revision after infection control. No significant between-group differences were observed in these complications.

Postoperative MSTS-93 scores were similar between the two groups (81% vs. 79%, p = 0.574). In contrast, the slotted stem group had a lower rate of end-of-stem pain than the control group (4.17% vs. 26.09%, p = 0.048). During follow-up, metastasis occurred in 2 patients in the slotted stem group and 1 patient in the control group, while local recurrence occurred in 1 patient in each group (Table 2).

Discussion

In this retrospective cohort study of pediatric patients undergoing uncemented distal femoral endoprosthetic reconstruction, the main findings were as follows. First, the slotted stem and conventional short stem showed comparable short-term aseptic loosening and complication rates. Second, the slotted stem was associated with less bone resorption in Zone 5. Third, the slotted stem group had a lower rate of end-of-stem pain, whereas overall functional outcomes measured by MSTS-93 were similar between groups.

Distal femoral endoprosthetic reconstruction offers several advantages for malignant bone tumours, including immediate structural stability, preservation of limb length, early mobilization, and restoration of function. For these reasons, it remains a widely used limb-salvage option in musculoskeletal oncology [26, 27]. However, bone resorption and subsequent aseptic loosening remain important causes of implant failure, and both are closely related to stem fixation and implant design.

At present, the two most commonly used fixation strategies for tumour endoprostheses are cemented fixation and biological press-fit fixation. Cemented prostheses provide immediate fixation by filling the gap between the stem and the host bone with bone cement, resulting in reliable short-term stability. However, long-term durability may be compromised by cement-related bone resorption. Unwin et al. reported a loosening rate of 9% after cemented distal femoral reconstruction at a mean follow-up of 45.7 months, whereas the 10-year loosening rate increased to 32.6% [28]. In another long-term study of Stanmore cemented prostheses for primary malignant bone tumours, the revision burden was substantial [29]. In contrast, uncemented press-fit prostheses may provide better long-term fixation through biological osseointegration. Batta et al. reported aseptic loosening rates of 15.72% at 5 years, 18% at 10 years, and 18% at 15 years in patients treated with uncemented prostheses [30], and Bus et al. reported a loosening rate of 15.5% at 15 years [31]. However, the success of uncemented fixation depends on sufficient initial stability and subsequent bone ingrowth. Several strategies have therefore been explored to improve stem fixation, including modifications in stem geometry and surface characteristics. Gong et al. reported favourable long-term osseointegration with curved HA-coated press-fit stems, with a prosthesis survival rate of 88% at 8.5 years and revision for loosening in only 7% of patients [10]. Moreover, Heesterbeek et al. reported that slotted stems can achieve short-term stability comparable to that of cemented stems, with no statistically significant difference in short-term loosening rates between the two [32]. In biomechanical studies have also demonstrated that slotted stems can avoid stress concentration and stress shielding, thereby reducing bone resorption and the risk of fractures [20, 21, 33].

These issues may be particularly relevant in pediatric patients. Compared with adults, children generally have shorter residual bone segments after tumour resection and narrower medullary canals, both of which make secure stem fixation more challenging. Existing modular systems are also largely derived from adult anatomical data and may not optimally match pediatric anatomy. The technical challenges associated with limb reconstruction in skeletally immature patients further highlight the importance of tailored surgical strategies and implant design optimization [22].

In the present study, the aseptic loosening rate was numerically lower in the slotted stem group than in the control group, but the difference was not statistically significant. Given the small sample size and limited follow-up, this finding should be interpreted cautiously. Rather than demonstrating superiority or formal non-inferiority, our results suggest that the slotted stem achieved short-term fixation performance comparable to that of the conventional HA-coated short stem in this cohort.

By contrast, bone resorption in Zone 5 was less frequent in the slotted stem group. A possible explanation is that the slotted structure reduces distal stiffness and allows more compliant load transfer, thereby decreasing stress shielding and stress concentration at the stem tip [34–36]. In addition, the compressible nature of the slotted segment may facilitate distal press-fit fixation with less aggressive reaming, which may reduce local bone loss [37–39]. These interpretations remain mechanistic hypotheses rather than direct proof and should be confirmed in future biomechanical and clinical studies. The lower rate of end-of-stem pain in the slotted stem group is also noteworthy and is consistent with previous reports [18, 19, 40]. This finding may be related to reduced distal stress concentration at the stem tip. In contrast, MSTS-93 scores were similar between groups. This suggests that the potential advantage of the slotted stem in this cohort may be more evident in distal stem-related symptoms and local bone preservation than in overall short-term functional status. This is not unexpected, as the MSTS-93 is a multidimensional functional scale and may be less sensitive to isolated differences in stem-tip discomfort over a relatively short follow-up period. The complication rates were not significantly different between the two groups. Because the number of events was limited, no firm conclusion should be drawn regarding infection risk differences between stem designs.

This study has several limitations. First, its retrospective single-center design introduces the possibility of selection bias and limits causal inference. Second, the sample size was small, which reduced statistical power, particularly for uncommon outcomes such as aseptic loosening. Third, the median follow-up of approximately 35 months is insufficient for reliable evaluation of long-term implant survival and late loosening. Fourth, multivariable adjustment for potential confounders such as tumour type, resection length, and chemotherapy-related factors was not performed, and residual confounding cannot be excluded. Finally, this study was not designed as a formal non-inferiority trial; therefore, the findings should be interpreted as preliminary comparative observations.

In conclusion, in this retrospective cohort, the slotted stem showed comparable short-term aseptic loosening and complication rates to the conventional short stem, with less Zone 5 bone resorption and a lower rate of end-of-stem pain. Slotted stems are viable alternatives to short stems for distal femoral endoprosthetic reconstruction following tumour resection in pediatric patients. Given the limited sample size, lack of multivariable adjustment, and relatively short follow-up, these findings should be considered preliminary and require confirmation in larger prospective studies.

Author contributions

CQ.T , L.M and MX.L contributed to the study design and supervision. Z.P, LL.T, Y.Z, ZZ.L and Y.L contributed to study design, data extraction and statistical, and manuscript draft，ZH.P, Y.L contributed to data extraction and response to reviewers. All authors contributed to data interpretation, reviewed the final work, and approved the submission.

Funding

This study was funded by 1·3·5 project for disciplines of excellence, West China Hospital, Sichuan University (ZYJC18036), Science and Technology Research Program of Sichuan Province (2020YFS0036), Young Scientists Fund of the National Natural Science Foundation of China(82402816).

Data availability

No datasets were generated or analysed during the current study.

Declarations

Ethics approval and consent to participate

This study was approved by the ethical committee of West China Hospital of Sichuan University (NO.2023(1692)). The requirement for informed consent was waived because of the retrospective nature of the study and the use of anonymized data.

Competing interests

The authors declare no competing interests.