Why does tension band wiring fail in transverse patellar fractures? Radiographic insights from a 10-years retrospective cohort

Abstract

Background

The aim of this study was to identify the radiographic parameters associated with failure of tension band wiring (TBW) in the treatment of transverse patellar fractures, with the goal of guiding surgical decision-making.

Materials and methods

A total of 76 patients underwent surgical treatment for patellar fractures at Trakya University between January 2013 and December 2022. We retrospectively analyzed 32 patients who met the study’s inclusion criteria for transverse fractures (AO Type 34- C1) treated with TBW. Radiographic parameters assessed included patellar width, inter-K-wire distance, K-wire-to-patella ratios, knot configuration, and K-wire length, all evaluated for their potential association with fixation failure. Failure was defined as cerclage wire slippage or breakage. Statistical analyses were conducted using SPSS and Jamovi software. Descriptive statistics, t-tests, chi-square or Fisher’s exact tests, logistic regression, and ROC analysis were performed. A p-value < 0.05 was considered significant.

Results

The mean age was 50 years ± 15.8 (range 26–80), with 8 women (25%) and 24 men (75%). Nine patients (28.1%) experienced TBW failure. Notably, single-knot constructs had significantly higher failure rates (66.7% vs. 19.2%; OR = 0.119, 95% CI [0.017–0.843], p = 0.038). Increased K-wire length was associated with failure (p = 0.008; cutoff 69.1 mm, AUC = 0.785). Patella–K-wire length ratio was higher in failures (p = 0.035). Lateral K-wire to articular distance and lateral K-wire to articular distance surface to patella thickness ratio were also significant predictors in slippage group (p = 0.046 and p = 0.031).

Conclusion

The number of knots, K-wire length, and specific radiographic parameters are important predictors of TBW failure. Attention to construct configuration and K-wire placement is crucial to minimize failure risk.

Introduction

Patellar fractures represent approximately 1% of all skeletal injuries, most commonly resulting from low-energy trauma, such as a fall directly onto the knee [1]. The most frequently observed fracture pattern is transverse pattern (56% − 62,9 AO type C) [2, 3]. Due to the variation in fracture types, individualized surgical planning and fixation techniques are often required.

Tension-band wiring (TBW) has been the most common way to treat patellar fractures. This technique works by turning the pulling forces from the thigh muscles and knee bending into compression at the joint surface, which helps the bone heal. Over time, different types of tension band wiring have been developed. The early methods included the standard tension band and the modified anterior tension band. Later, surgeons created another version that uses long K-wires and a figure-of-8 stainless steel wire wrapped over the front of the patella [4]. This TBW method remains the standard surgical approach for displaced transverse patellar fractures [5, 6].

Despite its widespread use, TBW is associated with significant complication rates. Specifically, complications have been reported to range from 5 to 47%, mainly due to loss of fixation, nonunion, or hardware breakage [7–9]. Symptomatic hardware irritation is also common, affecting up to 60% of patients, and often leads to implant removal, with secondary surgery rates reported between 37% and 50% [8–11]. Although secondary surgery rates are high, this issue was not the primary focus of our study.

Previous literature has highlighted high complication rates with TBW, yet few studies have systematically examined the impact of radiographic and technical factors on failure [12–15]. Hsu et al. reported that tension band placement influences loss of reduction and implant breakage, indirectly supporting the notion that excessive lateral K-wire placement compromises construct stability [7]. However, their study did not provide predictive thresholds or assess K-wire length. Similarly, while Neumann-Langen et al. and Berninger et al. documented high implant-related complication rates, they did not evaluate wire placement or length as predictors of failure [16, 17].

Therefore, the aim of this study was to identify patient and radiographic factors associated with TBW failure in transverse patellar fractures, specifically examining variables such as weight, BMI, patellar size, K-wire placement and length, tension band knot position, and the spatial relationships and ratios between K-wires and the patella.

Materials and methods

This retrospective study was conducted at Trakya University Faculty of Medicine and included patients who underwent surgical treatment for patellar fractures between January 2013 and December 2022. Out of 76 patients operated on during this period. Inclusion criteria were transverse patellar fracture (AO Type 34-C1), fixation with classic tension band wiring (TBW), and a minimum radiological follow-up of 12 months. Exclusion criteria were open fractures, fractures involving the superior or inferior pole, and, circular cerclage wiring, combinations of circular cerclage wiring with TBW, cannulated screws, or combined techniques involving TBW and other fixation methods. A total of 18 fractures were excluded due to being comminuted fracture, 6 fractures were vertical fractures, 7 were transverse fractures treated with cannulated screws, 3 were treated with plate fixation, 3 were treated using suture materials such as PDS or Ethibond, 1 patient underwent partial patellectomy, and 6 patients were excluded due to lack of 12-month follow-up. As a result, 32 patients with transverse fractures treated exclusively with tension band wiring were included in the final analysis.

Radiographic assessment was performed using standard anteroposterior and lateral knee radiographs. The following parameters were measured: weight, height, body mass index (BMI), patellar width; inter-K-wire distance; K-wire to patellar width ratio; number of bent K-wire ends (single or both); location of the tension band knot (central or corner); distance the end of proximal K-wire to tension band wire; number of knots; distance of the knot from the corner; patellar length; K-wire length; patellar length to K-wire length ratio; patellar thickness; distance between the K-wire and the articular surface; and patellar thickness to K-wire–articular distance ratio (Fig. 1). Additionally, age and sex were recorded for all patients. All radiographic measurements were independently performed by two orthopedic surgeons to ensure reliability.

Fig. 1.

Knee AP and lateral X-ray, a) patellar width, b) inter-K-wire distance, c) distance the proximal end of proximal K-wire to tension band wire, d) distance the distal end of proximal K-wire to tension band wire, e) distance of the knot from the corner, f) K-wire length, g) patellar length, x) patellar thickness, y) distance between the K-wire and the articular surface

Failure was defined as either cerclage wire slippage from one end of the K-wire or breakage of the wire construct. The timing and mode of failure were recorded for each patient.

Statistical analyses were conducted using SPSS (version 27; IBM Corp., Armonk, NY) and Jamovi (version 2.6; Jamovi Project, Sydney, Australia). Descriptive statistics were reported as mean ± standard deviation (SD) or median (interquartile range, IQR) for continuous variables, and as counts and percentages for categorical variables. Independent samples t-tests or Mann-Whitney U tests were used to compare continuous variables, while the chi-square test or Fisher’s exact test was used for categorical variables. Logistic regression analysis and receiver operating characteristic (ROC) curve analysis were performed to assess the predictive performance of key radiographic parameters. Statistical significance was set at p < 0.05.

The study was approved by the Trakya University Faculty of Medicine Ethics Committee (approval number: 11/35, 03.05.2024).Written informed consent was obtained from all hospitalized patients.

Results

The mean age was 50 years (sd:15.8; range 26–80), with 8 women (25%) and 24 men (75%). TBW failure occurred in nine patients (28.1%). The failures included six cerclage wire slippages and three wire breakages. The median time to failure was 58 days. Among these failures, slippage was the predominant mechanism, observed in six patients with a median time to occurrence of 33 days.

The mean height of all patients was 171.1 ± 8.41 cm, with a mean weight of 80.7 ± 13.04 kg and a mean BMI of 27.54 ± 3.9 kg/m². There was no significant difference in BMI between the loosening group (29.72 ± 4.29) and the non-loosening group (26.76 ± 3.54), p = 0.065. There was also no significant difference in height between the loosening group (172.25 ± 10.10 cm) and the non-loosening group (170.68 ± 7.94 cm), p = 0.66. However, there was a significant difference in weight between the groups, with the loosening group (88.50 ± 16.31 kg) being heavier than the non-loosening group (77.86 ± 10.71 kg), p = 0.046.

When analyzed by sex, female patients had a mean height of 164.87 ± 3.72 cm and a mean weight of 77.87 ± 12.45 kg, resulting in a mean BMI of 28.68 ± 4.71 kg/m². Male patients had a mean height of 173.36 ± 8.54 cm and a mean weight of 81.72 ± 13.04 kg, with a mean BMI of 27.13 ± 3.60 kg/m². There was no significant difference in BMI (p = 0.344) or weight (p = 0.484) between female and male patients. However, male patients were significantly taller than female patients (p = 0.012). Gender was not associated with failure (p = 0.82).

In our study, etiological analysis of patellar fractures revealed a diverse spectrum of injury mechanisms: 10 cases were due to traffic accidents, 7 resulted from high-energy falls from height, 7 were work-related injuries, 6 were caused by direct trauma to the patella, and 9 occurred following low-energy falls.

The number of knots was significantly associated with tension band loosening. Participants in the single-knot group exhibited a significantly higher rate of loosening compared to those in the double-knot group (66.7% vs. 19.2%, p = 0.038). Binary logistic analysis revealed that the odds of loosening were 8.4 times higher in the single-knot group compared to the double-knot group (OR = 0.119, 95% CI [0.017, 0.843], p = 0.038).

The location of the knot (corner vs. central) was not significantly associated with tension band loosening p = 0.243. The number of bent K-wire ends (single vs. both ends) showed no significant association with loosening p = 0.149.

Participants who experienced tension band loosening had significantly longer K-wire lengths compared to those without loosening (mean difference − 12.40 mm; 95% CI [–21.33, − 3.48]; t(30) = − 2.84; p = 0.008). ROC curve analysis identified an optimal cutoff value of 69.1 mm for K-wire length in predicting tension band loosening, yielding a sensitivity of 77.8% and specificity of 73.9% (Youden Index = 0.517; AUC = 0.785, p = 0.013), indicating good discriminative power. The patella-to-K-wire length ratio was significantly lower in the failure group compared to the non-failure group (0.70 ± 0.08 vs. 0.77 ± 0.07; p = 0.035). Other parameters (patella width, K-wire distance, distance the end of proximal K-wire to tension band wire, patella length) were not significant (Table 1).

Table 1.

Radiological parameter comparison in patients with and without tension band failure

Radiological parameters	Failure group Mean (Std.) N = 9	Non-failure group Median (Std.) N = 23	p value
Patella width	56.3 (6.09)	52.3 (6.66)	0.159
Distance between K-wires	20.1 (6.58)	16.8 (6.1)	0.190
Distance between K wires to patella width ratio	0.35 (0.1)	0.31 (0.1)	0.328
Distance of proximal K-wire to cortex	7.65 (3.8)	6.03 (2.6)	0.179
Distance of knot from cortex	13.06 (5.42)	10.55 (7.77)	0.383
Lateral view K wire distance to articular surface	10.83 (2.95)	9.71 (2.89)	0.337
K wire distance to articular surface to patella thickness ratio	0.43 (0.08)	0.42 (0.1)	0.835
K wire length	77.75 (12.12)	65.35 (10.71)	0.008
Patella length	54.36 (8.02)	49.97 (5.54)	0.086
Patella length to K wire length ratio	0.7 (0.08)	0.77 (0.07)	0.035

Std.: Standard deviation

Subgroup analysis of the failed cases demonstrated that the lateral distance from the K-wire to the articular surface was significantly greater in the slippage group compared to the non-slippage group (12.15 ± 2.65 mm vs. 9.54 ± 2.78 mm). Receiver operating characteristic (ROC) analysis showed good discriminative ability of this parameter for predicting cerclage wire slippage, with an area under the curve (AUC) of 0.792 (p = 0.046). The optimal cutoff value was identified as 10.85 mm, providing a sensitivity of 83.3% and a specificity of 73.1% (Youden Index = 0.564).

Similarly, analysis of the ratio between the K-wire distance to the articular surface and patellar thickness revealed that this ratio was significantly higher in the slippage group than in the non-slippage group (0.48 ± 0.04 vs. 0.41 ± 0.10). ROC analysis demonstrated moderate discriminative ability for this ratio in predicting slippage, with an AUC of 0.676 (p = 0.031). The optimal cutoff value was determined as 0.45, yielding a sensitivity of 83.3% and a specificity of 65.4% (Youden Index = 0.487). These ROC analyses are presented in Fig. 2.

Fig. 2.

Receiver operating characteristic (ROC) curves for predictors of K wire-cerclage wire slippage

Discussion

This retrospective study evaluated the radiographic and technical factors associated with failure of tension band wiring (TBW) in the treatment of transverse patellar fractures. Among 32 patients, we observed a failure rate of 28.1%, with most failures (66.7%) due to cerclage wire slippage and the remainder due to wire breakage. This rate aligns with previously reported TBW failure rates, ranging from 15.6 to 56% depending on patient population and surgical technique [17, 18].

The key finding of this study was the identification of two radiographic parameters—K-wire length and lateral K-wire to articular surface distance—as significant predictors of TBW failure. To our knowledge, this is the first clinical study to provide optimal cutoff values for these parameters (69.1 mm for K-wire length; 10.85 mm for lateral K-wire to articular surface distance) using receiver operating characteristic (ROC) analysis. These quantitative thresholds offer practical intraoperative guidance to optimize fixation and minimize failure risk.

Previous studies have documented the high complication rates associated with TBW fixation but have rarely examined the influence of specific radiographic or technical factors on failure risk [12–17]. Our findings build upon this literature by demonstrating that excessive lateral placement and increased length of K-wires can be objectively measured and directly linked to construct failure. While Hsu et al. suggested that tension band positioning affects implant stability, they did not establish predictive thresholds or evaluate K-wire length as an independent risk factor, which represents a novel aspect of our study.

Unexpectedly, we found that failure was associated with longer K-wire lengths, challenging the conventional assumption that insufficient wire length compromises stability. This result suggests that disproportionately long K-wires may increase the mechanical lever arm, leading to micromotion, soft tissue irritation, or increased stress concentration at the fixation site, predisposing the construct to slippage and instability. This finding is consistent with the TRON group analysis [13]. This interpretation is further supported by the significantly lower patella length to K-wire length ratio observed in the failure group, indicating a mismatch between implant length and patellar dimensions. These findings emphasize the importance of achieving an optimal proportional relationship between K-wire length and patellar anatomy, rather than simply prioritizing longer implants.

Additionally, neither knot location (central vs. corner) nor the number of bent K-wire ends showed a significant association with failure. This contrasts with some studies suggesting that knot positioning or K-wire bending affects stress distribution [19, 20]. However, the number of knots was a significant predictor in our analysis, with single-knot constructs exhibiting an 8.4-fold higher failure risk than double-knot constructs. This finding underscores the importance of redundancy and reinforcement in knotting techniques to enhance construct durability.

While male patients were significantly taller than female patients, no significant sex differences were observed in BMI or weight, and failure rates did not differ by sex. This suggests that the radiographic risk factors identified for TBW failure in this study are unlikely to be substantially influenced by sex-based morphological differences. Interestingly, our results showed that patients who experienced tension band loosening had significantly higher body weight compared to those without loosening (88.5 ± 16.31 kg vs. 77.86 ± 10.71 kg, p = 0.046), despite no significant differences in BMI or height. This finding indicates that absolute body weight, rather than BMI, may place greater mechanical load on the fixation construct, thereby increasing the risk of loosening. Although BMI reflects relative weight to height, the total force generated by heavier individuals during activities of daily living may predispose the tension band construct to mechanical failure.

Based on World Health Organization classifications, the mean BMI of both male and female patients falls within the overweight category. Although none of the groups had a mean BMI reaching the obesity threshold, the relatively high prevalence of overweight status in this cohort may have contributed to the observed mechanical loading effects on fixation stability.

In our study, most patellar fractures were caused by high-energy trauma mechanisms, including motorcycle accidents, work-related injuries, and falls from height. This etiological distribution differs from the broader literature, where low-energy falls in elderly female patients are often reported as the predominant cause [3]. The predominance of high-energy injuries in our cohort likely explains the relatively low number of female patients observed,

Recent trends in patellar fracture management have explored non-metallic fixation techniques and orthobiologic augmentation to reduce implant-related complications and improve healing outcomes [21, 22]. Yet, the inherent complexity of these fractures continues to challenge consensus regarding the optimal fixation technique and construct configuration [23, 24].

While our findings reinforce the importance of precise technical execution in TBW, it is important to note emerging strategies aiming to mitigate the limitations inherent to metallic implants. Non-metallic suture-based constructs and bioabsorbable fixation systems have been proposed to decrease symptomatic hardware removal rates and postoperative irritation [21, 22]. Orthobiologic augmentation with platelet-rich plasma or mesenchymal stem cell injections has been reported in conjunction with suture-based fixation, potentially enhancing biological healing in challenging cases such as nonunions [21]. Recent biomechanical reviews suggest that non-metallic alternatives may provide improved outcomes, although robust clinical trials remain lacking [25].

Our findings have several important clinical implications. First, intraoperative radiographic assessment of K-wire length and lateral positioning is critical to achieving durable fixation. Surgeons should aim for a K-wire length not exceeding 69 mm and a lateral K-wire to articular distance below 10.85 mm to minimize mechanical insufficiency. Second, the observed association between lower patella-to-K-wire length ratio and failure highlights the need for patient-specific implant selection and careful intraoperative tailoring based on patellar morphology. Third, our data raise important considerations about the inherent limitations of classic TBW constructs. Given the high complication rates reported across studies, alternative fixation strategies, such as plating systems or cannulated screw-based tension band constructs, may warrant consideration, particularly in patients with challenging anatomy or fracture characteristics [26, 27].

Limitations and future directions

This study has several limitations. Its retrospective design and single-center setting may limit external validity [28]. Firstly, the modest sample size precluded the performance of multivariable logistic regression analyses to adjust for potential confounding variables or to identify independent predictors of fixation failure. As a result, only univariable analyses were performed, limiting the ability to draw firm conclusions regarding causality. Additionally, the sample size and the predominance of male patients prevented meaningful subgroup analyses to evaluate sex-based differences in failure rates.

ROC analyses provided useful cutoff values for predicting fixation failure but these should be interpreted with caution. Due to the modest sample size, multivariable analyses could not be performed to adjust for potential confounding variables, limiting the ability to establish these cutoffs as independent predictors. To minimize confounding, this study deliberately included only a single fracture type (transverse fractures) and a single treatment method (classic tension band wiring) to reduce heterogeneity related to fracture morphology and fixation technique.

Functional outcomes were not assessed, preventing correlation of radiographic findings with patient-reported or clinical measures. Moreover, the findings are specific to transverse fractures treated with classic TBW and may not extrapolate to comminuted fractures or alternative fixation methods.

Future research should aim to validate these radiographic thresholds in larger, multicenter prospective cohorts. Biomechanical studies using patient-specific 3D models could further clarify the relationship between K-wire length, patellar morphology, and construct stability [29]. Randomized controlled trials comparing traditional TBW with alternative constructs—such as cannulated screw-based tension bands or plate fixation—are needed to provide high-level evidence guiding surgical decision-making.

Future investigations should also explore the integration of non-metallic fixation constructs and orthobiologic adjuvants to further optimize patellar fracture healing and reduce hardware-related complications [21, 22, 25].

Conclusion

In conclusion, this study provides novel quantitative insights into radiographic predictors of TBW failure in transverse patellar fractures. By identifying K-wire length and lateral placement as modifiable risk factors, our findings offer actionable intraoperative guidance for optimizing fixation stability. Meticulous surgical technique, including achieving anatomical reduction, precise implant positioning, and appropriate knot configuration, remains critical to minimizing failure risk. Future prospective studies with larger sample sizes are warranted to validate these results and inform surgical decision-making. Consideration of alternative or modified fixation strategies may further enhance outcomes in selected patients.

Author contributions

Idea/concept and design: E.S.; Data collection and/or processing: F.C., S.K.; Control/supervision and analysis and/or interpretation: E.S.; Literature review: E.S., M.E., S.Y.; Writing the article: E.S. Critical review: E.S., M.E., References: F.C., S.K.; Materials: S.Y.

Funding

The authors received no financial support for the research.

Data availability

The data that support the findings of this study are available from the corresponding author upon reasonable request.

Declarations

Ethics approval and consent to participate

The study protocol was approved by the Trakya University Faculty of Medicine Scientific Research Ethics Committee (approval number: 11/35, 03.05.2024). The study was conducted in accordance with the principles of the Declaration of Helsinki. Written informed consent was obtained from all hospitalized patients.

Consent for publication

The authors and participants confirm that they consent to the publication of this article.

Competing interests

The authors declare no competing interests.