Abstract: We included five small trials involving 169 participants with patella fractures. Participant age ranged from 16 to 76 years. There were 68 females and 100 males; the gender of one participant was not reported. Two trials were conducted in China and one each in Finland, Mexico and Turkey. All five trials compared different surgical interventions. Two trials compared biodegradable versus metallic implants for treating displaced patella fractures; one trial compared patellectomy with advancement of vastus medialis obliquus versus simple patellectomy for treating comminuted patella fractures; and two trials compared percutaneous osteosynthesis (both procedures were 'novel' and one used a new device) versus open surgery for treating displaced patella fractures. All the trials had design flaws, such as lack of assessor blinding, which put them at high risk of bias, potentially limiting the reliability of their findings. No trial reported on health-related quality of life, return to previous activity or cosmetic appearance. Very low quality evidence from two trials (48 participants) comparing biodegradable versus metallic implants indicated little difference between the two interventions at two-year follow-up in the numbers of participants with occasional knee pain (1/23 versus 2/24), incurring adverse events (3/24 versus 1/24) or with reduced knee motion (2/23 versus 2/24). Neither trial reported patient-rated knee function scores. In one trial, as per routine practice, metallic implants were removed one year after surgery (four participants). The other trial did not report on this aspect. Very low quality evidence from one trial (28 participants) indicated that compared with simple patellectomy, patellectomy with advancement of vastus medialis obliquus surgery for treating comminuted patella fractures resulted in more participants with a 'good' result based on a subjectively rated score (12/12 versus 11/16; risk ratio (RR) 1.42, 95% confidence interval (CI) 1.01 to 2.01), fewer participants experiencing knee pain (5/12 versus 13/16; RR 3.11, 95% CI 1.01 to 9.60) and more participants with unlimited activity and no loss in quadriceps strength at four-year follow-up. The only adverse event reported was a patellar tendon subluxation in the simple patellectomy group. Neither trial comparing percutaneous osteosynthesis (using novel devices or methods) versus open surgery reported on patient-rated knee function scores. Very low quality evidence from two trials (93 participants) showed that percutaneous osteosynthesis improved knee pain measured using visual analogue scale (0 to 10 where 10 is worst pain) at one month (mean difference (MD) -2.24, 95% CI -2.80 to -1.68) and at up to three months (MD -1.87, 95% CI -2.45 to -1.29). This effect did not persist at six months (very low quality evidence from one trial). Very low quality evidence from the two trials showed significantly fewer participants with adverse events (loss of reduction, infection, hardware complications, delayed wound healing) after percutaneous surgery (8/47 versus 28/46; RR 0.28, 95% CI 0.14 to 0.55). Very low quality evidence from the two trials indicated better clinician-rated knee function scores after percutaneous fixation at two to three months and 12 months follow-up; however, the between-group difference was not clinically important at 24 months. Very low quality evidence showed a lower incidence of hardware removal in the percutaneous group at two years; however, the results in the two trials were heterogeneous and the reasons for removal were not given in detail. There is very limited evidence from RCTs about the relative effects of different surgical interventions for treating fractures of the patella in adults. There is no evidence from RCTs evaluating the relative effects of surgical versus conservative treatment or different types of conservative interventions. Based on very low quality evidence, biodegradable implants seem to be no better than metallic implants for displaced patellar fractures; patellectomy with vastus medialis obliquus advancement may give better results than simple patellectomy for comminuted patellar fractures; and two novel methods of percutaneous osteosynthesis may give better results than conventional open surgery. However, until conclusive evidence becomes available, treatment options must be chosen on an individual patient basis, carefully considering the relative benefits and harms of each intervention and patient preferences. Further randomised trials are needed, but in order to optimise research effort, these should be preceded by research that aims to identify priority questions.

Plain-language summary: We searched the scientific literature up to May 2014 and found five relevant studies with a total of 169 participants. Participants in these studies were aged between 16 and 76 years. There were 68 females and 100 males; the gender of one participant was not reported. Two studies were conducted in China, and one each in Finland, Mexico and Turkey. All five studies compared different types of surgery or surgical devices. Thus, we found no studies comparing different types of conservative treatment or surgery versus conservative treatment. The five studies made three comparisons. We judged the evidence available for each comparison was of very low quality. This was because all the trials had design flaws that put them at high risk of bias and the studies were also too small. What the included studies found None of the studies reported on health-related quality of life, return to previous activity or cosmetic appearance. Two studies comparing biodegradable (non-metallic) versus metallic implants found little difference in outcomes (knee pain, adverse events and function) between the two groups. Neither study reported on patient-rated function. One study compared patellectomy with repositioning of a tendon with simple patellectomy (kneecap is removed) for treating complex kneecap fractures. It found that tendon repositioning resulted in more participants reporting better knee function and fewer participants with pain and limited knee function. One participant had an adverse event. Two studies found that novel methods of percutaneous fixation (surgery using small incisions to insert the fixation devices) resulted in less knee pain and fewer adverse events (mainly relating to the fracture fixation materials) than open surgery (involving wide incisions). Neither study reported on patient-rated function. Conclusions Overall, the evidence is very low quality and is insufficient to draw firm conclusions about the best method of treatment for kneecap fractures. Treatment options must be chosen on an individual patient basis, carefully considering the relative benefits and harms of each intervention and patient preferences. Further research is warranted and should be preceded by research to determine which questions should be prioritised.