Simon Ben-Avi

Reconstruction of the Coracoclavicular Ligaments with Tendon Grafts A Comparative Biomechanical Study

Background Numerous surgical techniques have been described to address injuries to the coracoclavicular ligaments. Purpose To compare the biomechanical properties of tendon graft reconstructions with those of the native coracoclavicular ligaments and various other repair methods. Study Design Controlled laboratory study. Methods Eleven fresh-frozen human cadaveric shoulders were tensile tested to failure to compare the biomechanical properties of the native coracoclavicular ligaments, coracoacromial ligament transfer, No. 5 Mersilene suture repair, 5-mm Mersilene tape repair, and tendon graft reconstructions with gracilis, semitendinosus, and long toe extensor tendons. Results Reconstructions with semitendinosus, gracilis, or long toe extensor tendon grafts were found to have superior initial biomechanical properties compared with coracoacromial ligament transfer; failure strengths were as strong as those of the native coracoclavicular ligaments. Failure of the tendon grafts occurred through the midsubstance of the tendon graft, not at the fixation site. Conclusions Tendon graft reconstruction may be an alternative to coracoacromial ligament transfer and may provide a permanent biologic reconstruction with superior initial biomechanical properties, including that of tensile strength. Clinical Relevance Use of tendon graft reconstruction may limit the need for postoperative immobilization and lead to an accelerated rehabilitation program.

Optimizing Achilles Tendon Repair: Effect of Epitendinous Suture Augmentation on the Strength of Achilles Tendon Repairs

Background Epitendinous suture augmentation has been shown to increase gap resistance and overall strength in flexor tendon repairs of the hand. The purpose of this study was to evaluate the effect of various suture augmentation techniques in Achilles tendon repair. Materials and Methods Eighteen fresh-frozen cadaveric Achilles tendons were transected and repaired with a 4-strand Krackow core stitch. Suture augmentation was performed with 3 figure-of-eight stitches in 6 specimens and a running cross-stitch weave in 6 specimens. The other 6 specimens were not augmented. Each tendon was loaded to failure on an MTS. Force to failure (defined as peak force or force at 5 mm gapping), gapping resistance, stiffness, and elongation were compared. Results Force to failure (p < 0.001), stiffness (p < 0.01) and gapping resistance (p < 0.05) were increased by suture augmentation. Additionally failure force and gapping resistance for the cross-stitch augmentation was higher than the figure-of-eight augmentation (p < 0.05). Conclusion Cross-stitch augmentation of Achilles tendon repair yields a stronger and stiffer repair with greater resistance to gapping. Clinical Relevance Achilles tendon repairs augmented with a cross stitch weave will be able to withstand substantially higher forces than non-augmented repairs.

Biomechanical Comparison of a Knotless Suture Anchor With Standard Suture Anchor in the Repair of Type II SLAP Tears

PURPOSE To compare the biomechanical strength of knotless suture anchors and standard suture anchors in the repair of type II SLAP tears. METHODS Five pairs of cadaveric shoulders (10 shoulders) were dissected free of soft tissue except for the glenoid labrum and long head of the biceps tendon. Type II SLAP tears were created and repaired with 1 of 2 anchors: the Mitek Lupine suture anchor or the Mitek Bioknotless suture anchor (DePuy Mitek, Raynham, MA). All specimens were preloaded to 10 N, and loaded for 25 cycles in 10 N increments to a maximum of 200 N. If specimens were still intact after 200 N, they were loaded to ultimate failure. The load at which 2 mm of gapping occurred, load to ultimate failure, mode of failure, and the number of cycles to failure were compared using the Wilcoxon signed-rank test. RESULTS Load to 2-mm gapping was lower (P = .042) for knotless anchors (70 N) versus knotted anchors (104 N), with similar differences for ultimate failure (74 N v 132 N; P = .043), cycles to 2-mm gapping (133 v 219 cycles; P = .042), and cycles to failure (143 v 297; P = .043). Eight of 10 specimens failed at the soft tissue interface (4 knotless, 4 knotted) and 2 failed by anchor pullout (1 knotted, 1 knotless). CONCLUSIONS The results of this study suggest that repair of a type II SLAP with a Mitek knotted suture anchor and mattress suture configuration through the biceps anchor is stronger than repair with a Mitek knotless suture anchor. The most likely method of repair failure was at the suture-soft tissue interface regardless of the type of anchor used. The application of a suture anchor that requires arthroscopic knot tying may be preferable to a knotless anchor for the surgical repair of type II SLAP tears. CLINICAL RELEVANCE Repair of type II SLAP tears with knotless suture anchors may allow for the avoidance of arthroscopic knot tying but is weaker than repair with standard suture anchors.

TRANSCUTANEOUS MAGNETIC STIMULATION OF THE QUADRICEPS VIA THE FEMORAL NERVE

We investigated the efficacy of different frequencies and intensities of magnetic stimulation for activating the quadriceps muscles; a painless method for stimulating the quadriceps would be useful in the rehabilitation of patients who have difficulty in voluntarily activating their muscles after injury or surgery. Eleven subjects underwent magnetic stimulation of the femoral nerve over a range of frequencies and intensities using a MagStim Rapid magnetic stimulator. Magnetic stimulation at 30 Hz at 80% of the power output of the stimulator used was capable of generating 72% of quadriceps maximal voluntary contraction torque. Subjects reported little or no pain during the procedure. Magnetic stimulation of the femoral nerve is a well‐tolerated way to activate the quadriceps muscles. Muscle Nerve 30: 379–381, 2004

Central Fatigue after Cycling Evaluated Using Peripheral Magnetic Stimulation

UNLABELLED Central and peripheral mechanisms contribute to fatigue during exercise. Electrical and transcranial magnetic stimulation have been used to assess these fatigue mechanisms. Peripheral magnetic stimulation (PMS) of the femoral nerve is associated with very little subject discomfort and has been shown to elicit quadriceps contractions of >70% maximal voluntary contraction (MVC). PURPOSE To examine peripheral versus central mechanisms of fatigue in men during prolonged cycling using a peripheral nerve magnetic stimulation-based technique. METHODS Eleven men (aged 41 +/- 3 yr) cycled for 2 h at approximately 66% of VO2peak (55 +/- 2 mL x kg(-1) x min(-1)) with five 1-min sprints interspersed, followed by a 3-km time trial. Oxygen consumption was measured every 20 min to verify a constant workload. RPE were measured simultaneously and during each sprint using a Borg scale. Quadriceps isometric strength testing was performed in a seated position before and after cycling: 1) MVC, 2) MVC with superimposed magnetic stimulation to measure central activation ratio (CAR), 3) femoral nerve stimulation alone. One-minute recoveries were allowed between contractions. Changes in metabolic measurements over time were analyzed with repeated-measures ANOVA, and strength changes before to after with Students paired t-tests. RESULTS HR (P = 0.03) and RPE (P < 0.001) increased over time during the 2 h, and MVC declined by 22% (P = 0.001) indicating fatigue. Force elicited by PMS alone decreased 17% (P < 0.001). CAR decreased from 83% before exercise to 71% (P = 0.005) after exercise indicating a loss of central drive. PMS-induced force was > or =90% of MVC. CONCLUSIONS Results clearly demonstrate that trained cyclists experience significant central fatigue during prolonged cycling. PMS may be a better technique for identifying central fatigue than the traditionally used interpolated twitch technique.