The increasing incidence of surgically treated quadriceps tendon ruptures

The most important finding of the present study was the steep increase in the annual incidence of operatively treated QTRs from 1997 to 2014. To the best of our knowledge, this is the first study to assess the nationwide incidence of surgically treated QTRs. During the 18-year study period, there was a 4.1-fold overall increase in the incidence of QTRs. Along with the increasing incidence of QTRs, especially in male patients, it was also evident that the mean age of the patients suffering this injury increased, because the increase in incidence was the most dramatic in patients aged 60 or more.

Huttunen et al. [11] reported that the overall incidence of ATRs in Sweden has risen steadily in recent years, and that there has also been a clear increase in the mean age of the patients suffering from the condition. One likely explanation for the increase in the mean age of patients sustaining an ATR is the growing number of older patients participating in high-demand sports [1, 3]. The more active life style of older patients may have also contributed to the findings in our study. In our study, the mean age of the male patients sustaining a QTR increased from 49.5 to 55.8 years during the 18-year study period. It is crucial to note, however, that QTR is rarely directly associated with participation in high-demand sports and is more often associated with a degenerative tendon or a simple fall [5, 9]. Naturally, a fall that results in QTR could very well happen during high-demand sports also. The aetiology of QTR could not, however, be evaluated from the available register data.

It can be postulated that a more active lifestyle plays a less important role in the changing epidemiology of QTR compared with that of ATR. As previously mentioned, QTR usually occurs after a simple fall and a sudden uncontrolled muscle contracture that results in a rupture in a degenerated tendon [15, 24]. Tendon degeneration is correlated with chronic illnesses, such as diabetes, hyperlipidemia, and thyroid disorder [2, 9, 14]. In a large series of patients with a knee extensor mechanism injury, Garner et al. reported that patients with QTR were more obese than those with a PF, which also commonly follows a simple fall [9]. The incidence of chronic diseases and obesity associated with QTR and PF has been steadily increasing at a national level [22]. Therefore, it is likely that, together with an increasing overall life expectancy, older patients are more vulnerable to conditions associated with degeneration, such as QTR.

The main limitation in our study was the lack of information regarding the possibility that the patient had undergone a total knee arthroplasty (TKA). QTR is a rare although devastating complication after TKA that occurs most commonly during the first months after surgery [4, 7]. Whereas spontaneous QTR is usually an endpoint in the tendon degeneration process, the predisposing factors after TKA include a possible iatrogenic injury to the tendon during surgery. Therefore, these two rupture types must be considered as different entities. The prevalence of QTR rupture in patients having undergone a TKA has ranged between 0.1 and 0.29% in two large cohort studies [4, 7]. During our study, the number of annual TKAs performed in Finland increased from 4279 in 1997 to 10,406 in 2014 [18]. Since 2006, the increase has plateaued with the number of annual TKAs varying between 9541 and 10,917. Assuming that the prevalence of QTR during the early postoperative period after TKA was as high as 0.29% in the Finnish population, the annual number of QTRs associated with TKA would range from 27 to 31 patients and would, therefore, not explain the increase seen in our study. Although the number of TKAs performed annually had possibly doubled during the study period, the extent of the contribution of QTR associated with TKA in the observed increase in the incidence of QTRs was small. The majority of the observed three-to-fivefold increase in incidence is, therefore, likely due to other factors.

Evidence for the optimal surgical treatment of patients sustaining a QTR is very limited. No randomised clinical trials (RCT) that have compared different surgical treatment methods have been published. An important part of treatment is also the postoperative regime, which can vary in both time and immobilisation method used. There is no evidence of the optimal postoperative treatment regime either. It is feasible and intuitive to choose the method of surgical repair according to the site of the tear. Paradoxically, while the incidence of QTR has risen remarkably, RCTs that compare different postoperative treatments are lacking. The patients sustaining a QTR are older than patients with other extensor mechanism injuries, such as patellar fracture or PTR. Therefore, these patients are more vulnerable to immobilisation-related comorbidities, such as venous thromboembolism and re-ruptures [21]. Moreover, due to their advanced age, these patients are also more prone to heterotopic ossification and deep infection, which may have devastating outcomes and long-term morbidity [21].

A further limitation in this study was the lack of complete data on comorbidities. Since these are incompletely recorded in the database, it was not possible to investigate the effects of comorbidities on the incidence of QTRs, of which diabetes and endocrine diseases would have been of most interest. The major strength of our study was the inclusion of nationwide data that minimised bias and increased robustness in the analysis leaving only coding errors as a main source of uncertainty and bias.

Based on data from the Finnish National Hospital Discharge Register, the annual incidence of QTR increased by 411% during the 18-year study period. The average age of the patients affected by the injury also increased. In total, 9 out of 10 QTRs occurred in male patients. QTR is very rarely treated without surgery, and thus, our study result can be considered to be a reliable estimate of the increase in the incidence of this injury.