Markus Wambacher

The medial periosteal hinge, a key structure in fractures of the proximal humerus: A BIOMECHANICAL CADAVER STUDY OF ITS MECHANICAL PROPERTIES

The medial periosteal hinge plays a key role in fractures of the head of the humerus, offering mechanical support during and after reduction and maintaining perfusion of the head by the vessels in the posteromedial periosteum. We have investigated the biomechanical properties of the medial periosteum in fractures of the proximal humerus using a standard model in 20 fresh-frozen cadaver specimens comparable in age, gender and bone mineral density. After creating the fracture, we displaced the humeral head medial or lateral to the shaft with controlled force until complete disruption of the posteromedial periosteum was recorded. As the quality of periosteum might be affected by age and bone quality, the results were correlated with the age and the local bone mineral density of the specimens measured with quantitative CT. Periosteal rupture started at a mean displacement of 2.96 mm (SD 2.92) with a mean load of 100.9 N (SD 47.1). The mean maximum load of 111.4 N (SD 42.5) was reached at a mean displacement of 4.9 mm (SD 4.2). The periosteum was completely ruptured at a mean displacement of 34.4 mm (SD 11.1). There was no significant difference in the mean distance to complete rupture for medial (mean 35.8 mm (SD 13.8)) or lateral (mean 33.0 mm (SD 8.2)) displacement (p = 0.589). The mean bone mineral density was 0.111 g/cm(3) (SD 0.035). A statistically significant but low correlation between bone mineral density and the maximum load uptake (r = 0.475, p = 0.034) was observed. This study showed that the posteromedial hinge is a mechanical structure capable of providing support for percutaneous reduction and stabilisation of a fracture by ligamentotaxis. Periosteal rupture started at a mean of about 3 mm and was completed by a mean displacement of just under 35 mm. The microvascular situation of the rupturing periosteum cannot be investigated with the current model.

A Randomized Study of the Effectiveness of Suprascapular Nerve Block in Patient Satisfaction and Outcome After Arthroscopic Subacromial Decompression

PURPOSE The purpose of this study was to evaluate the efficiency of the suprascapular nerve (SSN) block in pain reduction after arthroscopic subacromial decompression operations and its influence on patient satisfaction. Furthermore, we wanted to evaluate whether better perioperative pain management could positively influence postoperative shoulder function. METHODS In this prospective, randomized, double-blinded clinical trial, 3 groups of patients--each with 15 participants--were treated with SSN block (10 mL of 1% ropivacaine), placebo, or a subacromial infiltration of local anesthesia (20 mL of 1% ropivacaine). Preoperative and postoperative pain was evaluated with a visual analog scale. Functional outcome was measured by the Constant-Murley score, and patient satisfaction was measured anecdotally by interview 2 days, 2 weeks, and 6 weeks after surgery. RESULTS The SSN group reported significantly lower levels of postoperative pain, required significantly less analgesia, had better range of motion, and had higher levels of postoperative satisfaction in comparison to the subacromial infiltration group and placebo group. CONCLUSIONS Patients treated with SSN blocks had less pain overall, which led to a decreased need for analgesics in comparison to the subacromial infiltration and placebo groups. Furthermore, patients in the SSN-blocked group achieved better postoperative ROM and were significantly more satisfied after surgery.

The relevance of neutral arm positioning for true ap-view X-ray to provide true projection of the humeral head shaft angle

IntroductionTextbooks commonly recommend using the true anterior–posterior (ap)-view with the patient’s arm in a sling and therefore in internal rotation (IR) for radiologic diagnostic assessment of the proximal humerus after trauma. However, IR or external rotation (ER) may affect the projection of the head shaft angle (HSA) and therefore bias the diagnostic conclusion significantly. We hypothesized that neutral rotation (NR) of the arm is mandatory for true ap-view to provide true projection of the HSA.Materials and methodsA simplified geometrical model of the proximal humerus was used to examine the influence of different arm positions and angulations of the central ray in relation to the projection of the HSA.ResultsBoth ER and IR misleadingly suggested an increased valgus angle. Simulating the true ap-view with the central ray in cranio-caudal direction, IR changed the projection of the HSA substantially.ConclusionIn conclusion, standard fixation of the patient’s arm in a shoulder sling in IR for true ap-view may result in an oblique projection, potentially leading to incorrect surgical implications. To prevent misdiagnosed valgus or varus angulation, NR of the arm should be obeyed when performing true ap-view X-ray. We, therefore, highly recommend to overcome the traditionally arm position, ensuring the true amount of dislocation to assure correct surgical implications and comparable follow-up examinations.

Reply letter to the editor regarding the biomechanical evaluation of semirigid implants

Dear Editor, The setup for this selective testing of implants was chosen for two reasons. First, we wanted to compare our results with those of an existing study which had tested the LCPPH using the same setup [1]. Second, we believe that this selective setup is the most appropriate one to reveal the biomechanical performance of implants on the proximal humerus. As stated, we do think that there are fracture situations with interfragmentary ligamentotaxis that are relatively stable after reduction. This is the type of fracture that was treated traditionally with percutaneous pins or more recently with the Humerus Block with good results. These fracture situations are not the subject of our study. In our testing, the IMC showed the lowest stiVness in all cases of load. Subsequently, throughout cyclic testing, it failed to maintain even the initially modest stiVness and showed the greatest loss in load reduction. Therefore, we concluded that it appears highly questionable that the IMC should be capable of stabilizing complex, highly unstable situations without interfragmentary ligamentotaxis. In an ethic commission approved prospective randomised clinical trial testing IMC versus HB, we treated severely dislocated isolated two-part (subcapital) proximal humerus fractures. Inclusion criteria were dislocation of more than half of the width of the shaft or an angulation of more than 45° between the head and the shaft fragment. Patients were randomly assigned to one of the two implants. In both groups all patients were female; mean age was comparable in both groups (70 years IMC/ 68 years HB). In this series of largely geriatric fractures (with concomitant poor bone quality), the IMC was not capable of Wxing the intraoperatively impacted fracture site in an acceptable position until healing had occurred. We stopped the study because of the high rate of severe complications of the IMC implant. About 60% of the IMC treated patients suVered severe, implant-related complications. To sum up, the IMC implant may work in relatively stable subcapital fractures with intact ligamentotaxis and little displacement. These fractures, according to our protocol, are mostly treated nonoperatively. However, in unstable situations with the aforementioned criteria, we failed to demonstrate suYcient holding strength of the implant as well in the biomechnical setup as in the clinical situation.