Dealing with small samples in football research.

In football research, 'small' trials with low statistical power are common. On the elite level, the inherently low number of participants obviously conflicts with the relevance of even tiny effects. However, general characteristics of football also contribute (e.g. multifactorially influenced and/or complex outcomes). Importantly, small sample sizes are problematic regardless of the study outcome with issues ranging from inconclusive results and low precision to unrepeatable 'discoveries' and overestimation of effect sizes. Therefore, meeting the calculated, target sample size is the first priority. If a suboptimal sample size must be accepted, a range of tools can improve insights. To begin with, some general aspects of data collection and analysis become more important and should be optimally implemented (e.g. reliability of measures). Building on this foundation, specific amendments are available on the levels of data collection (e.g. aggregated single-subject designs) and data analysis (e.g. Bayesian methods). The present commentary aims to give an overview of selected, practical tools for dealing with small sample sizes in football research and provide recommendations for their application in scenarios typical for the field. Importantly, versatility and adaptability are mirrored by the need for utmost transparency including a predetermined (ideally preregistered) study plan. Collaboration or counselling with an expert statistician is strongly encouraged.

Dwarfs on the Shoulders of Giants: Bayesian Analysis With Informative Priors in Elite Sports Research and Decision Making.

While sample sizes in elite sports are necessarily small, so are the effects that may be relevant. This conundrum is complicated by an understandable reluctance of athletes to comply with extensive study requirements. In Bayesian analyses, pre-existing knowledge (e.g., from sub-elite trials) can be formally included to supplement scarce data. Moreover, some design specifics for small sample research extend to the extreme case of a single subject. This provides the basis for actionable feedback (e.g., about individual responses) thereby incentivising participation. As a proof-of-concept, we conducted a replicated cross-over trial on the effect of cold-water immersion (CWI) on sprint performance recovery in soccer players. Times for 30 m linear sprint and the initial 5 m section, respectively, were measured by light gates before and 24 h after induction of fatigue. Data were analysed by Bayesian and by standard frequentist methods. Informative priors are based on a published metaanalysis. Seven players completed the trial. Sprint performance was 4.156 ± 0.193 s for 30 m linear sprint and 0.978 ± 0.064 s for the initial 5 m section. CWI improved recovery of sprint time for the initial 5 m section (difference to control: -0.060 ± 0.060 s, p = 0.004) but not for the full 30 m sprint (0.002 ± 0.115 s, p = 0.959), with general agreement between Bayesian and frequentist interval estimates. On the individual level, relevant differences between analytical approaches were present for most players. Changes in the two performance measures are correlated (p = 0.009) with a fairly good reproducibility of individual response patterns. Bayesian analyses with informative priors may be a practicable and meaningful option particularly for very small samples and when the analytical aim is decision making (use / don't use in the specific setting) rather than generalizable inference.

Additional acromioclavicular cerclage limits lateral tilt of the scapula in patients with arthroscopically assisted coracoclavicular ligament reconstruction.

INTRODUCTION: The current treatment for acromioclavicular (AC) dislocation lacks a gold standard and previous literature concludes that coracoclavicular (CC) fixation with additional AC cerclage fixation adds stability and is a useful adjunct to augment these repairs. AIM: The purpose of this study was to investigate the clinical and radiological value of an additional AC cerclage. It was hypothesised that an additional AC cerclage would show better clinical results. We further expected the additional AC cerclage to result in lower radiological loss of reduction compared to the technique relying on CC-fixation only. METHODS: A total of 30 male patients with acute (less than 3 weeks) AC-dislocations Rockwood grade IV and V from 2013 to 2014 underwent arthroscopic bi-cortical CC-ligament reconstruction. Patients were assigned to a surgeon depending on the day of clinical presentation. One surgeon used only bi-cortical CC-ligament reconstruction (no-PDS group); the other surgeons used an additional PDS cerclage with an 8-loop configuration over the AC joint (PDS group). Clinical data (Constant Shoulder Score, ASES Score, DASH Score, VAS pain) were assessed 24 months post-operatively, and AP shoulder radiographs used to measure the AC and CC distances. RESULTS: No significant differences in the Constant (Z = - 0.498, p = 0.624), ASES (Z = 0.263, p = 0.806) and DASH (Z = 1.097, p = 0.305) score as well as VAS pain (Z = 0.498, p = 0.624) were seen for both groups. Factorial ANOVA showed a significant effect of "time" [F(1,28) = 17.54, p < 0.001, r = 0.62], reflecting a significant radiological increase of AC distances over time for both groups. Comparing CC and CC + AC groups, the effect of "OP technique" was significant [F(1,28) = 4.67, p = 0.039, r = 0.38], with AC distances obtained in the PDS group being statistically lower than in the No-PDS group, whereas CC distances did not significantly increase in both groups [F(1,28) = 0.07, p = 0.791]. "Time × OP technique" interaction effects were non-significant [F(1,28) = 0.38, p = 0.545], which reflects similar changes in AC distances over time in both groups. For the CC distances, neither main nor interaction effects were significant (all p > 0.05). CONCLUSION: Both the isolated CC reconstruction and the CC reconstruction with an additional AC cerclage showed good clinical results at 2 years' follow-up. AC distances increased in both groups from the post-surgery measurement to the 2-year follow-up, but were generally lower with an additional AC cerclage. CC distances did not increase significantly over time in both groups. Therefore, the presented data suggest adding a fixation of the AC joint.

Significant Improvement in Shoulder Function and Pain in Patients Following Biologic Augmentation of Revision Arthroscopic Rotator Cuff Repair Using an Autologous Fibrin Scaffold and Bone Marrow Aspirate Derived From the Proximal Humerus.

PURPOSE: To clinically evaluate patients who underwent a biologic augmentation technique in revision arthroscopic rotator cuff repair using an autologous fibrin scaffold and concentrated stem cells isolated from bone marrow aspirate (BMA) obtained from the proximal humerus. METHODS: This is a retrospective review of prospectively collected data from patients who underwent biologic augmentation of revision arthroscopic rotator cuff repair using an autologous fibrin scaffold and BMA obtained from the proximal humerus between 2014 and 2015. Minimum follow-up was 12 months. Outcome measures were collected preoperatively and postoperatively including range of motion as well as American Shoulder and Elbow Surgeons Shoulder Form, Simple Shoulder Test, single assessment numeric evaluation, and visual analog score. In addition, BMA samples of each patient were assessed for the number of nucleated cells and colony-forming units. Regression analysis was performed to investigate whether the number of nucleated cells and colony-forming units had an influence on outcome and failure. RESULTS: Ten patients who underwent biologic augmentation of revision arthroscopic rotator cuff repair using an autologous fibrin scaffold and concentrated BMA obtained from the proximal humerus between 2014 and 2015 were included. The mean follow-up time was 30.7 (range: 12-49) months. Four patients were revised at final follow-up. Postoperative clinical scores improved significantly: American Shoulder and Elbow Surgeons (28.1 ± 5.4 to 60.9 ± 9.0; P < .01), single assessment numeric evaluation (6.6 ± 2.3 to 65.1 ± 10.9; P < .01), visual analog scale (7.2 ± 0.9 to 3.1 ± 0.9; P < .01), and Simple Shoulder Test (1.6 ± 0.5 to 10.3 ± 5.7; P < .01). Postoperative range of motion increased significantly with regard to flexion (97.0 ± 13.6 to 151.0 ± 12.2; P < .01) and abduction (88.0 ± 14.0 to 134.0 ± 15.1; P = .038) but not with external rotation (38.0 ± 5.7 to 50.5 ± 6.5; P = .16). Less pain was correlated to an increased number of nucleated cells (P = .026); however, there was no correlation between failure rate and number of nucleated cells (P = .430). CONCLUSIONS: Patients who underwent biologic augmentation of revision arthroscopic rotator cuff repair using an autologous fibrin scaffold and concentrated BMA demonstrated a significant improvement in shoulder function along with reduction of pain. However, the overall revision rate for this procedure was 40%. LEVEL OF EVIDENCE: Level IV, therapeutic case series.

Distal femoral torsional osteotomy increases the contact pressure of the medial patellofemoral joint in biomechanical analysis.

PURPOSE: Torsional osteotomy of the distal femur allows anatomic treatment of patellofemoral instability and patellofemoral pain syndrome in cases of increased femoral antetorsion. The purpose of this study was to investigate the effects of distal femoral torsional osteotomy on pressure distribution of the medial and lateral patellar facet. METHODS: Nine fresh frozen human knee specimens were embedded in custom-made 3D-printed casts and tested with a robotic arm. Torsional osteotomy could be simulated ranging from increased femoral antetorsion of 25° with a corresponding lateralization of the patella to an overcorrected value of 5° of femoral antetorsion. The peak and mean lateral and medial compartment pressure was measured in 0°, 15°, 30°, 45°, 60° and 90° flexion beginning with neutral anatomic muscle rotation. RESULTS: The medial aspect of the patella showed a significant influence of femoral torsion with an increase of mean and peak pressure in all flexion angles with progressive derotation from 15° external rotation to 5° internal rotation (p = 0.004). The overall pressure difference was highest in near extension and stayed on a constant level with further flexion. On the lateral facet, the derotation resulted in decrease of pressure in near extension; however, it had no significant influence on the mean and peak pressure through the different torsion angles (n.s.). Unlike on the medial facet, a significant consistent increase of peak pressure from 0° to 90° flexion could be shown (p = 0.022) on the lateral patella aspect. CONCLUSION: Distal femoral torsional osteotomy to correct pathological femoral antetorsion leads to a redistribution of retropatellar pressure. External derotation leads to an increased peak pressure on the medial patellar facet and can impair simultaneous cartilage repair. However, as the lateral patellofemoral load decreases, it has a potential in preventing patellofemoral osteoarthritis.