Brent G. Parks

Stem Cell-Bearing Suture Improves Achilles Tendon Healing in a Rat Model

Background: Tendon healing is a slow and complicated process that results in inferior structural and functional properties when compared to healthy tendon tissue. It may be possible to improve outcomes of tendon healing with enhancement of biological aspects of the repair including tissue structure, organization, and composition. The purpose of this study was to determine whether use of a stem cell-bearing suture improves Achilles tendon healing in a rat model. Methods: The Achilles tendon was transected in 108 bilateral hind limbs from 54 rats. Each limb was randomized to repair with suture only (SO), suture plus injection (SI) of mesenchymal stem cells (MSCs) at the repair site, or suture loaded with MSCs (suture with stem cells, SCS). One half of the animals were randomly sacrificed at 14 and 28 days after surgery and the Achilles tendon was harvested. From each repair group at each time point, 12 limbs were randomized to biomechanical testing and 6 to histologic analysis. Tendons were loaded using a 223-N load cell at 0.17 mm/s. A blinded pathologist scored the histology sections. Results: Ultimate failure strength (N/mm2) was significantly higher in the SI and SCS groups versus the SO group. In the SI group, ultimate failure strength decreased significantly at 28 days versus 14 days. Histology score in the SCS group was significantly lower (better) than in both other groups (P ≤ .001). Histology findings at day 28 were significantly higher versus day 14 for all groups (P = .01). Conclusions: Both the SI and the SCS groups had significantly higher ultimate failure strength versus the SO group, and strength was maintained at 28 days in the SCS group but not in the SI group. Histology in the SCS group was significantly better than in both other groups. Clinical Relevance: These findings in a rat model suggest that the use of stem cells enhances healing after Achilles repair and that embedding of stem cells directly into suture offers sustained early benefit to tendon healing.

Stability of Acute Dorsal Fracture Dislocations of the Proximal Interphalangeal Joint: A Biomechanical Study

PURPOSEnWe performed a cadaveric biomechanical study to characterize proximal interphalangeal joint stability after an injury to different amounts of the volar articular base of the middle phalanx (intact, 20%, 40%, 60%, and 80% volar defects).nnnMETHODSnEighteen digits on 6 hands were tested through full proximal interphalangeal joint range of motion using computer-controlled flexion and extension via the digital tendons. We collected proximal interphalangeal joint kinematic cine data in a true lateral projection with mini-fluoroscopy. We measured the amount of dorsal middle phalanx translation in full proximal interphalangeal joint extension. As we cycled the joint from full flexion into extension, we recorded the angle at which subluxation occurred.nnnRESULTSnNo specimens with 20% volar bony defect subluxated. All specimens in the 60% and 80% groups subluxated at an average flexion angle of 67° (range, 10° to 90°) in the 60% group and at all degrees of flexion in the 80% group. In the 40% group, 28% of specimens demonstrated subluxation at an average flexion angle of 14° (range, 4° to 40°). Mean dorsal translation of the middle phalanx in relation to the proximal phalanx at full digital extension was 0.2 mm in the 20% group, 0.8 mm in the 40% group, 3.2 mm in the 60% group, and 3.1xa0mm in the 80% group.nnnCONCLUSIONSnSimulated volar articular bony defects of 20% were stable, whereas those with 60% and 80% defects were unstable during digital motion. Stability in the 40% group was variable and appeared to be the threshold for stability.nnnCLINICAL RELEVANCEnKnowledge of the typical amount of middle phalanx defect and degree of proximal interphalangeal joint extension that can lead to joint instability may improve management of mechanically important proximal interphalangeal joint fracture dislocations.

Stability of Fixation of Proximal Phalanx Unicondylar Fractures of the Hand: A Biomechanical Cadaver Study

PURPOSEnTo determine the relative stability of various fixation methods for proximal phalanx intra-articular unicondylar fractures during simulated early active motion.nnnMETHODSnWe created proximal phalangeal intra-articular unicondylar fractures in 13 fresh-frozen human cadaveric hands. Using a saw through a dorsal approach, we made an osteotomy beginning in the intercondylar notch and extending proximally at a 45° angle to the radial border of the proximal phalanx. We fixed each of the 4 fingers on each hand with a 1.5-mm headless compression screw, a 1.5-mm lag screw, two 1.1-mm smooth K-wires, or one 1.1-mm smooth K-wire. We rotated the order of constructs randomly for each hand. We simulated active range of motion on a custom-loading device at 0.25 Hz from full finger extension to full flexion for 2,000 cycles and measured displacement by a differential variable reluctance transducer.nnnRESULTSnWe found no significant differences in displacement of the fracture site among the 4 methods of fixation. Movement in the control specimen with no osteotomy fixation was significantly higher than with each of the other fixation methods.nnnCONCLUSIONSnBiomechanical stability did not differ among the fixation methods for proximal phalanx unicondylar fractures in a flexion-extension active range of motion model.nnnCLINICAL RELEVANCEnFixation of these fractures with any of the methods tested may provide sufficient stability to withstand postoperative therapy when there is no substantial resistance to active motion.

Torsional stability of the femur after harvest of the medial femoral condyle corticocancellous flap

BACKGROUNDnIncreasingly large segments of medial femoral condyle (MFC) corticocancellous flaps have been harvested for transfer. Biomechanical evaluations demonstrated no osseous stability impairment under axial loading regardless of flap size harvested. The purpose of this study was to determine the donor sites response to torsional forces.nnnMETHODSnDual-energy X-ray absorptiometry (DEXA) scanning was performed on 16 pairs of cadaver legs followed by removal of all soft tissues, except knee capsule and ligaments. Specimens were randomly assigned to three groups with bone harvest defects measuring 3, 5, or 7 cm in length and a control group with no osseous resection. Torsional load was applied until fracture or ligamentous failure.nnnRESULTSnBone failure rates were 12.5, 12.5, 28.6, and 55.6% for control, 3, 5, and 7 cm groups, respectively. Bone failure rate increased with increasing harvest size; the 7 cm group demonstrated a significantly higher rate compared with the other groups combined (55.6 vs. 17.4%; p = 0.03). Failure torque was 45.5, 29.35, 27.4, and 30.83 Nm for the control, 3, 5, and 7 cm groups, respectively (p = 0.11). Harvest of any size segment resulted in a significant decrease in failure torque (p = 0.01). Bone mineral density (BMD) and Z-scores were no different among groups (p = 0.79 and 0.59, respectively). A direct relationship was identified between force required for failure and BMD (p = 0.02) and Z-scores (p = 0.05) but not for failure location and BMD (p = 0.09) or Z-scores (p = 0.94).nnnCONCLUSIONnMFC corticocancellous flap harvest of any size decreases donor site failure torque. Flap harvests > 7 cm demonstrate a higher frequency of iatrogenic fracture and therefore warrant caution with torsional loading of the knee postoperatively. Routine preoperative DEXA scans may not be warranted.

Biomechanical Characteristics of Hemi-Hamate Reconstruction Versus Volar Plate Arthroplasty in the Treatment of Dorsal Fracture Dislocations of the Proximal Interphalangeal Joint

PURPOSEnTo compare stability and range of motion after hemi-hamate reconstruction versus volar plate arthroplasty in a biomechanical proximal interphalangeal (PIP) joint fracture-dislocation model.nnnMETHODSnEighteen digits from 6 cadaver hands were tested. We created defects of 40%, 60%, and 80% in the palmar base of each digits middle phalanx, simulating an acute PIP joint fracture-dislocation. Each defect scenario was reconstructed with a hemi-hamate arthroplasty followed by a volar plate arthroplasty. A computer-controlled mechanism was used to bring each digits PIP joint from full extension to full flexion via the digital tendons in each testing state, and in thexa0intact state. During each testing scenario we collected PIP joint cinedata in a true lateral projection using mini-fluoroscopy. A digital radiography program was used to measure the amount of middle phalanx dorsal translation (subluxation) in full PIP joint extension. We recorded the angle at which subluxation, if present, occurred during each testing scenario.nnnRESULTSnAverage dorsal displacement of the middle phalanx in relation to the proximal phalanx was 0.01 mm for the hemi-hamate reconstructed joints and -0.03 mm for the volar plate arthroplasty, compared with the intact state. Flexion contractures were noted in each of the specimens reconstructed with volar plate arthroplasty. Degree of contracture was directly correlated with defect size, averaging 20° for 40% defects, 35° for 60% defects, and 60° for 80% defects. We observed no flexion contractures in the hemi-hamate reconstructions.nnnCONCLUSIONSnSurgeons can use both hemi-hamate and volar plate arthroplasty to restore PIP joint stability following a fracture dislocation with a large middle phalanx palmar base defect. Use of volar plate arthroplasty led to an increasing flexion contracture as the middle phalanx palmar base defect increased.nnnCLINICAL RELEVANCEnClinicians can use the information from this study to help with surgical decision-making and patient education.

A knotless bidirectional-barbed tendon repair is inferior to conventional 4-strand repairs in cyclic loading

We divided 21 flexor digitorum profundus tendons in the index, middle and ring fingers in seven cadaver hands into three groups. The tendons were cut in zone 2 and repaired using a 4-strand cruciate core suture repair with one of the following three materials in each group: (1) a knotless repair with a 2-0 bidirectional-barbed suture, which has similar tensile strength as a 4-0 non-barbed suture used in the other two groups; (2) a knotted locking repair with a non-barbed 4-0 conventional suture; and (3) a non-locking repair with a non-barbed 4-0 knotless suture. The repaired fingers were cyclically loaded through a simulated active range of motion to a 5u2009N load. We monitored and recorded the gap sizes at regular intervals during the test. The 2-0 bidirectional-barbed suture group and non-barbed suture groups developed gaps of 2.2u2009mm after 10 cycles and 2.4u2009mm after 20 cycles, respectively. Over 1000 cycles, the mean gaps were 3.2u2009mm in the 4-0 conventional suture group and 9.1u2009mm in the 2-0 bidirectional-barbed group. The tendons in the 2-0 bidirectional-barbed group gapped earlier, with statistically significant differences compared with those in the locking repair with a non-barbed 4-0 knotless suture group. The repair strength of the barbed suture technique was inferior to the cruciate repairs using a conventional 4-0 non-barbed suture tested in this cyclic-loading model. Level of evidence: Level V

Safe Zone for Neural Structures in Medial Displacement Calcaneal Osteotomy A Cadaveric and Radiographic Investigation

Background: We aimed to define reference lines on standard lateral ankle radiographs that could be used intraoperatively to minimize iatrogenic nerve injury risk in medial displacement calcaneal osteotomy. Methods: Forty cadaveric specimens were used. In 20 specimens, the sural, medial plantar (MP), and lateral plantar (LP) nerves were sutured to radiopaque wire, and a lateral ankle radiograph was obtained. On the radiograph, a line was drawn from the posterior superior apex of the calcaneal tuberosity to the origin of the plantar fascia and labeled as the “landmark line.” A parallel line was drawn 2 mm posterior to the most posterior nerve, and the area between these lines was defined as the safe zone. In 20 additional specimens, an osteotomy was performed 1 cm anterior to the landmark line using a percutaneous or open technique. Dissection was performed to assess for laceration of the sural, MP, LP, medial calcaneal (MC), or lateral calcaneal (LC) nerves. Results: The safe zone was determined to be within the area 11.2 ± 2.7 mm anterior to the landmark line. After open osteotomy, lacerations were found in 3 of 10 MC nerves and 3 of 10 LC nerves. After percutaneous osteotomy, lacerations were found in 2 of 10 MC nerves and 1 of 10 LC nerves. No lacerations of the sural, MP, or LP nerves were found with either osteotomy. Conclusions: The safe zone extended 11.2 ± 2.7 mm anterior to the described landmark line. The MC and LC nerves were always at risk during medial displacement calcaneal osteotomy. Clinical Relevance: Nerve injury to both major and minor sensory nerves is likely underrecognized as a source of morbidity after calcaneal osteotomy. The current study provides a ready intraoperative guideline for minimizing this risk.

Biomechanical Analysis of Distal Clavicle Excision With Acromioclavicular Joint Reconstruction

Background: Acromioclavicular (AC) joint separation is a common injury, usually affecting young adults. Controversy exists regarding whether to excise the distal clavicle when surgical intervention is required. Purpose: To evaluate the biomechanical strength of AC and coracoclavicular (CC) ligament reconstruction with and without concurrent distal clavicle excision. Study Design: Controlled laboratory study. Methods: Nine matched pairs of cadaver shoulders were used. All shoulders were tested with intact CC and AC ligaments, and the ligaments were sectioned. For 1 shoulder in each pair, a 7-mm distal clavicle excision was performed. The contralateral distal clavicle was left intact. Single-tunnel CC ligament reconstruction was performed, and excess graft length was extended and secured across the AC joint to reconstruct the superior AC joint ligaments in all specimens. Specimens were then potted and cyclically loaded for 500 cycles in the anterior-posterior and superior-inferior planes using an MTS Minibionix load frame to evaluate displacement across the AC joint. Results: Regarding the clavicle–intact reconstructed versus the intact state, there was significantly greater AC joint translation in the reconstructed state in the anterior-posterior (20.2 ± 7.0 mm vs 6.0 ± 1.5 mm; P < .001) and superior-inferior directions (12.3 ± 3.3 mm vs 4.2 ± 1.2 mm; P < .001). In the clavicle–excised reconstructed versus the intact state, there was also significantly greater translation in the reconstructed state in the anterior-posterior (21.7 ± 5.1 mm vs 8.9 ± 4.3 mm; P < .001) and superior-inferior directions (12.3 ± 6.1 mm vs 5.8 ± 3.1 mm; P < .001). When the difference in translation between the reconstructed and intact groups in the clavicle-intact versus the clavicle-excised group was compared, no statistically significant difference was noted in anterior-posterior (14.2 ± 7.8 mm vs 12.8 ± 5.0 mm; P = .67) or superior-inferior translation (8.1 ± 2.9 mm vs 6.6 ± 3.9 mm; P = .39). Conclusion: Excision of the distal clavicle did not have a significant effect on anterior-posterior or superior-inferior motion at the AC joint following single-tunnel CC and AC ligament reconstruction. Clinical Relevance: The study suggests that excision of the distal clavicle in this procedure is not associated with increased anterior-posterior or superior-inferior instability in this model.

Early Weightbearing After Operatively Treated Ankle Fractures: A Biomechanical Analysis.

Background: No consensus exists regarding the timing of weightbearing after surgical fixation of unstable traumatic ankle fractures. We evaluated fracture displacement and timing of displacement with simulated early weightbearing in a cadaveric model. Methods: Twenty-four fresh-frozen lower extremities were assigned to Group 1, bimalleolar ankle fracture (n=6); Group 2, trimalleolar ankle fracture with unfixed small posterior malleolar fracture (n=9); or Group 3, trimalleolar ankle fracture with fixed large posterior malleolar fracture (n=9) and tested with axial compressive load at 3 Hz from 0 to 1000 N for 250 000 cycles to simulate 5 weeks of full weightbearing. Displacement was measured by differential variable reluctance transducer. Results: The average motion at all fracture sites in all groups was significantly less than 1 mm (P < .05). Group 1 displacement of the lateral and medial malleolus fracture was 0.1±0.1 mm and 0.4±0.4 mm, respectively. Group 2 displacement of the lateral, medial, and posterior malleolar fracture was 0.6±0.4 mm, 0.5±0.4 mm, and 0.5±0.6 mm, respectively. Group 3 displacement of the lateral, medial, and posterior malleolar fracture was 0.1±0.1 mm, 0.5±0.7 mm, and 0.5±0.4 mm, respectively. The majority of displacement (64.0% to 92.3%) occurred in the first 50 000 cycles. There was no correlation between fracture displacement and bone mineral density. Conclusion: No significant fracture displacement, no hardware failure, and no new fractures occurred in a cadaveric model of early weightbearing in unstable ankle fracture after open reduction and internal fixation. Clinical Relevance: This study supports further investigation of early weightbearing postoperative protocols after fixation of unstable ankle fractures.

Effect of Distal Ulnar Collateral Ligament Tear Pattern on Contact Forces and Valgus Stability in the Posteromedial Compartment of the Elbow

Background: It is not known whether the pattern of ulnar collateral ligament (UCL) tear affects elbow biomechanics. Hypothesis: There will be a significant change in elbow biomechanics with 50% proximal but not 50% distal simulated rupture of the UCL. Study Design: Controlled laboratory study. Methods: Pressure sensors in the posteromedial elbow joint of 25 male cadaveric elbows (average age, 54.9 years; range, 26-66 years) were used to measure contact area, pressure, and valgus torque at 90° and 30° of elbow flexion. Thirteen specimens were tested with the UCL intact, then with proximal-to-distal detachment of 50%, and then with proximal-to-distal detachment of 100% of the anterior band of the UCL from the ulnar attachment. This method was repeated in the remaining 12 specimens in a distal-to-proximal direction. Results: With 50% proximal-to-distal detachment, contact area decreased significantly versus intact at 90° (91.3 ± 23.6 vs 112.2 ± 26.0 mm2; P < .001) and 30° (69.3 ± 14.8 vs 83.1 ± 21.6 mm2; P < .001) of elbow flexion; the center of pressure (COP) moved significantly proximally versus intact at 90° (3.8 ± 2.5 vs 5.4 ± 2.3 mm; P < .001) and 30° (5.9 ± 2.8 vs 7.4±1.9 mm; P < .001). With 50% distal-to-proximal UCL detachment versus intact, no significant change was observed in contact area, movement of the COP, or valgus laxity at either flexion position. With 100% proximal-to-distal and distal-to-proximal detachment, significant change in contact area, movement of the COP, and valgus laxity versus intact was found at 90° and 30° of elbow flexion (P < .05). No significant difference in contact pressure was observed in any test conditions. Conclusion: Significant change in contact area and proximal movement of the COP with 50% proximal UCL detachment and the lack of significant change with 50% distal UCL detachment suggest that the proximal half of the UCL ulnar footprint has a primary role in maintaining posteromedial elbow biomechanics. Clinical Relevance: The findings suggest that surgical reconstruction should aim to reestablish at least the proximal 50% of the UCL ulnar footprint.