The long-term biomechanical and viscoelastic performance of repairing anterior cruciate ligament after hemitransection injury in a goat model

Fibrin-Based Biomaterial Systems to Enhance Anterior Cruciate Ligament Healing

Anterior cruciate ligament (ACL) tears are a common and potentially career-ending injury, particularly for athletes and soldiers. Partial and complete ruptures of this ligament cause instability in the knee, and the ACL does not have the capacity for healing due, in part, to its position within the highly thrombolytic synovial fluid environment of the knee joint. Traditional methods of ACL reconstruction, such as graft replacement with attached bone anchors for bone integration, restore stability, but do not prevent the development of post-traumatic osteoarthritis. To enhance therapeutic treatment options, novel fibrin-based technologies and repair techniques have been recently explored and show promise for improved patient outcomes. Through modification of existing surgical methods, such as the use of fibrin glues incorporating growth factors and cells and the implementation of scaffolds containing platelet-rich plasma, platelet-rich fibrin, and other blood derivatives, surgeons are attempting to overcome the shortcomings of traditional treatments. This mini-review will detail current efforts using fibrin-based treatments and discuss opportunities to further enhance ACL healing.

Effects of Unilateral Electroacupuncture on Bilateral Proprioception in a Unilateral Anterior Cruciate Ligament Injury Model

BACKGROUND Anterior cruciate ligament (ACL) injury can cause knee proprioception degeneration, on which the electroacupuncture (EA) treatment has a definite effect. However, it is still not clear whether conducting EA intervention on the injured side can promote bilateral proprioception recovery. MATERIAL AND METHODS We randomly selected 6 of 9 normal cynomolgus monkeys to develop unilateral ACL injury models via arthroscopy. All knees were divided into 5 groups: the normal control (NC) group, injured side of blank model (ISBM) group, contralateral side of blank model (CSBM) group, injured side of EA (ISE) group, and contralateral side of EA (CSE) group. Ten days after modeling, the monkeys in the EA group were treated with EA daily for 6 weeks at the acupoints. At 6 weeks, the 5 groups were examined by electrophysiology (SEPs and MCV). The ACL was separated to conduct the gold chloride staining for morphology observation and count the number of total and variant proprioceptors. RESULTS At 6 weeks, the latent period of the SEPs and MCV and the number of variant proprioceptors in the blank model group and the EA group were increased compared with the NC group, while the amplitude and the number of total proprioceptors were decreased. The changes in the ISBM and CSBM group were more remarkable than in the ISE and CSE group. All differences were statistically significant (P<0.05). CONCLUSIONS Unilateral ACL injury leads to bilateral proprioception degeneration, and the unilateral knee EA intervention can aid bilateral proprioception recovery.

Central defect type partial ACL injury model on goat knees: the effect of infrapatellar fat pad excision

Background

The mid-substance central defect injury has been used to investigate the primary healing capacity of the anterior cruciate ligament (ACL) in a goat model. The sagittal plane stability on this model has not been confirmed, and possible effects of fat pad excision on healing have not been evaluated. We hypothesize that excising the fat pad tissue results in poorer ligament healing as assessed histologically and decreased tensile strength of the healing ligament. We further hypothesize that the creation of a central defect does not affect sagittal plane knee stability.

Methods

A mid-substance central defect was created with a 4-mm arthroscopic punch in the ACLs of right knees of all the subjects through a medial mini-arthrotomy. Goats were assigned to groups based on whether the fat pad was preserved (group 1, n = 5) or excised completely (group 2, n = 5). The left knees served as controls in each goat. Histopathology of the defect area along with measurement of type I collagen in one goat from each group were performed at 10th week postoperatively. The remaining knees were evaluated biomechanically at the 12th week, by measuring anterior tibial translation (ATT) of the knee joints at 90° of flexion and testing tensile properties (ultimate tensile load (UTL), ultimate elongation (UE), stiffness (S), failure mode (FM)) of the femur-ACL-tibia complex.

Results and discussion

Histopathology analysis revealed that the central defect area was fully filled macroscopically and microscopically. However, myxoid degeneration and fibrosis were observed in group 2 and increased collagen type I content was noted in group 2. There were no significant differences within and between groups in terms of ATT values (p = 0.715 and p = 0.149, respectively). There were no significance between or within groups in terms of ultimate tensile load and ultimate elongation; however, group 2 demonstrated greater stiffness than group 1 that was correlated with the fibrotic changes detected microscopically (p = 0.043).

Conclusions

The central defect type injury model was confirmed to be biomechanically stable in a goat model. Resection of the fat pad was noted to negatively affect defect healing and increase ligament stiffness in the central defect injury model.

Anterior tibiofemoral intersegmental forces during landing are predicted by passive restraint measures in women

BACKGROUND

Passive restraint capabilities may influence sagittal plane knee joint mechanics during activity. This study aimed to determine if measures associated with passive restraint of anterior translation of the tibia are predictive of peak anterior knee shear force during landing.

METHODS

Passive restraint measures were assessed via joint arthrometry and during 40% body weight simulated weight acceptance using recreationally active students (73F, 42M; 21.8±2.9yr, 1.69±0.1m, 68.9±14.1kg). Anterior knee laxity (mm) at 133N and initial (0-20N) and terminal (100-130N) anterior stiffnesses (N/mm) were calculated from arthrometer data. Peak anterior tibial acceleration (m∙s(-2)) relative to the femur was assessed via electromagnetic position sensors during 40% body weight acceptance trials. Peak knee shear force was assessed during double-leg drop jumps.

RESULTS

Sex specific linear stepwise regressions revealed that in females, increasing peak tibial acceleration (5.1±1.8m·s(-2)) (R(2)∆=7.3%, P∆=0.021), increasing initial anterior stiffness (31.0±14.0N/mm) (R(2)∆=5.9%, P∆=0.032), and decreasing terminal anterior stiffness (43.4±17.4N/mm) (R(2)∆=4.9%, P∆=0.046) collectively predicted greater peak knee shear forces (66.6±12.03% BW) (multiple R(2)=18.1%). No male regressions were significant.

CONCLUSIONS

Sagittal laxity measures are associated with anterior knee shear loads during landing in females. Greater tibial acceleration during early axial load along with greater initial and lesser terminal anterior stiffnesses predicted increasing anterior knee shear forces. Future work should investigate the combined contribution of passive and active restraints to high-risk ACL biomechanics.

Anterior knee stiffness changes in laxity "responders" versus "nonresponders" across the menstrual cycle

CONTEXT

Although changes in anterior knee laxity (AKL) across the menstrual cycle have been reported, the effects of cyclic knee laxity changes on the underlying characteristics of the load-displacement (stiffness) curve generated during anterior loading of the tibia relative to the femur are relatively unknown.

OBJECTIVE

To describe the anterior load-displacement curve during anterior loading of the tibia relative to the femur using incremental stiffnesses and to compare underlying stiffness measures between days of the cycle when AKL is at its minimum and maximum.

DESIGN

Descriptive laboratory study.

SETTING

University laboratory.

PATIENTS OR OTHER PARTICIPANTS

Fifty-seven recreationally active women.

MAIN OUTCOME MEASURE(S)

Anterior knee laxity and 6 incremental stiffness measures (N/mm) were obtained with an instrumented knee arthrometer on days 1-6 of menses and days 0-8 postovulation during 2 consecutive menstrual cycles. Participants were then classified in tertiles based on the maximum change (difference between maximum and minimum) in AKL, and incremental stiffness was compared on days of minimum versus maximum laxity between the lowest (<1.24 mm cyclic laxity change = laxity "nonresponders" [n = 19]) and highest (>1.75 mm cyclic laxity change = laxity "responders" [n = 19]) tertiles.

RESULTS

All participants displayed decreasing stiffness initially (0-20 N > 20-40 N and 40-60 N), followed by incrementally increasing stiffness (40-60 N < 60-80 N < 80-100 N < 100-130 N) (P ≤ .05). Responders demonstrated decreased stiffness between the days of minimum and maximum AKL at the 10-130-N increment versus the 0-20-N and 20-40-N increments (P ≤ .05); nonresponders had no change in stiffness.

CONCLUSIONS

Participants who experienced larger magnitudes of cyclic changes in AKL also experienced decreases in terminal (100-130 N) stiffness during anterior knee joint loading. Decreases in incremental stiffness at higher anterior directed loads may adversely affect passive restraint systems, resulting in altered arthrokinematics during functional activity.

Biomechanical evaluation of augmented and nonaugmented primary repair of the anterior cruciate ligament: an in vivo animal study

PURPOSE

The purpose of this study was to evaluate in a sheep model the biomechanical performance of augmented and nonaugmented primary repair of the anterior cruciate ligament (ACL) following transection at the femoral end during a 12-month postoperative observation.

METHODS

Forty sheep were randomly assigned to nonaugmented or augmented primary ACL repair using a polyethylene terephthalate (PET) band. At two, six, 16, 26 and 52 weeks postoperatively four sheep in each group were sacrificed and biomechanical testing performed.

RESULTS

Compared with nonaugmented primary ACL repair, the PET-augmented repair demonstrated superior biomechanical results from 16 weeks postoperatively onwards in terms of anterioposterior (AP) laxity, tensile strength and ligament stiffness. The augmentation device works as a stress shield during the ligament healing process. The nonaugmented ACL repair also resulted in ligament healing, but the biomechanical properties were at a significantly lower level.

CONCLUSION

These results support the previously reported histological findings following augmented primary ACL repair. This animal study on the healing capacity of the ACL may provide some important contributions to how primary healing in certain types of ruptures can be achieved.

CLINICAL RELEVANCE

I.

Changes in serum collagen markers, IGF-I, and knee joint laxity across the menstrual cycle

Variations in serum markers of collagen production (CICP) and degradation (ICTP), insulin-like growth factor I (IGF-I) and anterior knee laxity (AKL) were measured in 20 women [10 with spontaneous cycles (eumenorrheic), 10 using oral contraceptives] over 5 consecutive days at menses (M1-M5, 1st pill week), the initial estrogen rise near ovulation (O1-O5, 2nd pill week), the initial progesterone rise of the early luteal phase (EL1-EL5, 3rd pill week) and post-progesterone peak of the late luteal phase (LL1-LL5, 4th pill week). ICTP was higher in oral contraceptive women (5.3 ± 1.7 vs. 3.7 ± 1.3 µg/L; p = 0.030), primarily during days near ovulation and the early luteal phase when concentrations decreased in eumenorrheic women (p = 0.04). IGF-I concentrations increased during menses then decreased and remained lower during the early and late luteal phase in oral contraceptive women, resulting in lower concentrations compared to eumenorrheic women at EL2 and LL1 (p = 0.03). CICP decreased in early and late luteal days (p <0.01), and there was a trend toward lower concentrations in eumenorrheic versus oral contraceptive women (85.7 ± 35.7 ng/ml vs. 123.2 ± 49.8 ng/ml; p = 0.07). Lower CICP and greater IGF-I concentrations predicted greater AKL across the 20 cycle days in both groups (R(2)  = 0.310 and 0.400). Sex hormone concentration changes across the menstrual cycle are of sufficient magnitude to influence collagen metabolism, and may indirectly influence knee structure and function.

Effects of a therapeutic laser and passive stretching program for treating tendon overuse

OBJECTIVE

This study investigated the effects of a therapeutic laser, passive stretching, and their combined treatment on the strength of Achilles tendons with overuse pathologies.

BACKGROUND DATA

Tendinopathy involving overuse is usually treated with exercise and stretching, but there has been no report on the treatment effect of a therapeutic laser combined with passive stretching on managing this condition. Despite the beneficial effect of a therapeutic laser on healing tendons that have had traumatic injury, its effect on degenerative tendons is not known.

METHODS

Twenty-five mature Sprague-Dawley (SD) rats were used, with 20 subjected to daily bipedal downhill running for 8 weeks, to induce Achilles overuse, and 5 as normal controls. The exercised rats were divided into four groups: 1, laser treatment; 2, passive stretching; 3, combined laser and stretching; and 4, no treatment, running controls. GaAlAs laser with 660 nm wavelength was applied to both Achilles tendons for 50 sec for Groups 1 and 3. Passive stretching of 20 times/10 sec of maximum ankle plantar flexion was applied to Groups 2 and 3. Treatments were applied after each running session for a a total of 56 treatment sessions. On week 9, the tendons were tested for load-relaxation, stiffness, and ultimate strength.

RESULTS

Stiffness was different (p=0.01), difference in ultimate strength was marginally insignificant (p=0.07), and load-relaxation difference was not significant among groups. Post-hoc analyses revealed that the mean stiffness of all the four exercise groups was lower than the normal control, whereas the ultimate strength from the laser and combined laser and stretching was not different from that of the normal control group, but was higher than that of the passive stretching and no treatment groups.

CONCLUSIONS

We conclude that a therapeutic laser and combined laser with passive stretching might slow down the decrease in Achilles tendon strength but would not be able to stop the pathological changes of overuse from developing.

Comparing therapeutic ultrasound with microamperage stimulation therapy for improving the strength of Achilles tendon repair

In exploring the effects of therapeutic ultrasound (US) and microamperage stimulation (MAS) on the biomechanical performance of repairing Achilles tendon in rats, 35 Sprague-Dawley rats receiving surgically induced injury to their right medial Achilles tendon were studied. The rats were divided into four groups of low-dose US (group 1, n = 10), high-dose US (group 2, n = 11), MAS (group 3, n = 7), and control (group 4, n = 7). The treatment started on day 6 after injury. Groups 1 and 2 received 4 min of daily US treatment at 1.0 and 2.0 W/cm(2), respectively. Group 3 received 30 min of daily transcutaneous MAS treatment. Group 4 received 30 min of daily sham MAS treatment. On day 31, the Achilles tendons were mechanically tested. Data on the right side were normalized to the left side and analyzed with MANOVA with α = 0.05. Results of MANOVA was significant and post hoc tests revealed that the normalized strength of groups 1, 2, and 3 were higher than that of group 4 (p = 0.003) but no significant difference was found among the treatment groups. The ANOVA result of the normalized load relaxation and stiffness was p = 0.06 and p = 0.07, respectively. These findings suggested that both low/high doses of US and MAS therapies could improve the strength of Achilles tendon but in view of its short treatment time, US is considered to be more efficient than MAS for improving the strength of the repairing tendons.

Enforced bipedal downhill running induces Achilles tendinosis in rats

Enforced downhill running has been reported to induce tendinosis in the rat supraspinatus tendon but similar exercise failed to induce Achilles tendinosis in this animal. Due to the presence of acromial arch in the shoulder, accessing the supraspinatus tendon with physical modalities is difficult; thus this model may not be suitable for studying the treatment for tendinosis. To develop a rat model for Achilles tendinosis, we tested 14 mature Sprague-Dawley rats by dividing them into 2 groups of 7 each. The experimental group was subjected to a daily enforced downhill bipedal running program by suspending their upper bodies so that they ran with their hind limbs on a treadmill for 1 hr/day for 8 weeks. The downward inclination was 20 degrees and the speed was 17 m/min. The animals in the control group did not undergo any exercise. After 8 weeks, the Achilles tendons were harvested and subjected to histological and biomechanical analysis. Histological examination revealed tenocyte proliferation, change in tenocytes appearance, and collagen bundle disintegration in the running group. The biomechanical testing revealed significant decrease in stiffness (p = 0.002) and ultimate tensile strength (p = 0.016) in the running group than in the control group. Both the histological and biomechanical findings are suggestive of changes in the tendon of the running group that resembled the pathological changes of tendinosis in human. This new model of Achilles tendinosis in rat will be useful for studying the etiology and subsequent management strategies of this condition.

Biologically enhanced ACL reconstruction

Biological integration of the tendon graft is a crucial prerequisite for successful ACL reconstruction. Histological studies showed that the human ACL remnants contain a cellular capacity for healing potential. The goal of this technical note is to describe an ACL reconstruction technique, using ACL remnants as a biological sleeve for the graft. In case of complete ACL rupture with a large remnant, the tibial tunnel was performed inside and through the ACL tibial stump by careful sequential drilling. Femoral tunnel placement was performed by an outside-in technique. The hamstring graft was kept attached to the tibia and routed through the ACL remnant to the femur. The aim of this technique is the preservation of the biological and mechanical properties of the ACL remnant. In order to preserve large remnants resulting in greater graft coverage, the best period to perform this reconstruction is during the first weeks after the injury.

Effect of bone morphogenetic protein-12 gene transfer on posterior cruciate ligament healing in a rabbit model

BACKGROUND

The posterior cruciate ligament heals to some extent after injury. However, results after conservative treatment may diminish with long-term follow-up. Bone morphogenetic protein-12 can induce formation of ligament tissues.

HYPOTHESIS

Bone morphogenetic protein-12 gene transfer can improve the histologic and biomechanical properties of healing posterior cruciate ligaments.

STUDY DESIGN

Controlled laboratory study.

METHODS

Bilateral posterior cruciate ligaments of 32 rabbits were injured. The cut ends in 1 limb received an injection containing 3 x 10(7) pfu recombinant bone morphogenetic protein-12 adenovirus, and the posterior cruciate ligament in the contralateral limb served as an untreated control. Eight rabbits were sacrificed at each time point of 3, 6, 12, and 26 weeks after the operation. In addition, 6 rabbits receiving a sham operation were used to obtain normal control data. The posterior cruciate ligament specimens were evaluated biomechanically and histologically.

RESULTS

The repair tissue of the treatment group at 26 weeks was similar to the normal posterior cruciate ligament in collagen arrangement, collagen formation, and mechanical properties. At weeks 6, 12, and 26, the ultimate load, stiffness, and energy absorbed at failure of the treatment group were significantly greater than those of the untreated group.

CONCLUSION

Adenovirus-mediated bone morphogenetic protein-12 gene transfer in a partial posterior cruciate ligament laceration rabbit model resulted in an obvious improvement of histologic properties, tensile strength, and stiffness of the repaired ligaments, indicating improved posterior cruciate ligament healing.

CLINICAL RELEVANCE

Bone morphogenetic protein-12 gene transfer is a potential future strategy to improve the repair of injured posterior cruciate ligaments.

Histological evaluation of the healing potential of the anterior cruciate ligament by means of augmented and non-augmented repair: an in vivo animal study

The purpose of this animal study was to investigate the healing potential of the anterior cruciate ligament following transaction at the femoral end, by means of both the augmented and the nonaugmented primary repair, focusing on the histological changes during a 12-month postoperative observation period with respect to necrosis and the loss of normal structures during the healing period. Twenty sheep were randomly assigned to nonaugmented primary ACL repair, or to augmented ACL repair using a polyethylene terephthalate (PET) band. At 2, 6, 16, 26 and 52 weeks postoperatively four sheep out of each group were sacrificed. Histological healing was achieved after 16 weeks for the augmented repair group and after 26 weeks for the nonaugmented repair group. The main difference between the two techniques was that the PET augmentation device protected the ligament from necrosis and ligamentization. In this group a consistently normal ligament was seen histologically during the entire postoperative observation period. The nonaugmented repaired ACLs underwent the processes of necrosis and ligamentization.

Ultrasound phonophoresis of panax notoginseng improves the strength of repairing ligament: a rat model

This study examined the phonophoretic effect of a therapeutic ultrasound coupled with a Panax notoginseng (PN) gel and compared it with a therapeutic ultrasound alone for medial collateral ligament repair in rats. Twenty mature male Sprague-Dawley rats receiving surgical transection to the left medial collateral ligament (MCL) were divided randomly into three groups: ultrasound (US, n = 7), ultrasound with PN coupling gel (PNUS, n = 7) and control (n = 6). The treatments started on day 3 after surgery for six days per week over a two-week period. The US group received 4 min of pulsed ultrasound (1 MHz) at the intensity of 0.5W/cm(2) with a normal ultrasonic coupling gel. The PNUS group received the same ultrasound treatment, but with a coupling gel that contained PN extract. The control group received a placebo ultrasound treatment similar to the other two groups. On day 17, the ligaments were mechanically tested for load-relaxation, stiffness and ultimate tensile strength (UTS). Values of the left side were normalized against that of the right side of each animal for analysis. Results revealed significantly higher normalized stiffness (p = 0.009) and UTS (p = 0.022) in the PNUS group than the other two groups, but insignificant difference in load-relaxation among all groups. This study reveals a positive ultrasonic phonophoretic effect of Panax notoginseng extract for improving the strength of ligament repair than ultrasound therapy alone.

Combining therapeutic laser and herbal remedy for treating ligament injury: an ultrastructural morphological study

OBJECTIVE

We examined the ultrastructural morphology (number of collagen fibrils, mean and mass-averaged diameter) of isolated and combined treatments of a therapeutic laser and herbs for medial collateral ligament (MCL) injury in rats.

MATERIALS AND METHODS

Twenty-eight rats, divided into seven groups: laser (L), herb (H), laser + herb (LH), laser control (LC), herb control (HC), laser sham (LS) and herb sham (HS), were studied. Right MCL of groups L, H, LH, LC and HC were transected, while that of LS and HS remained intact. Group L received 9 treatment sessions of GaAlAs laser with a dosage of 3.5 Jcm(-2); group H received herbal plaster treatment; groups LH had combined treatments of laser and herb; group LC had placebo laser; group LS had no treatment; groups HC and HS received only bandage without herb. All MCLs were analyzed using transmission electron microscopy at 3 weeks.

RESULTS

Differences (p < 0.05) existed in mean fibril diameters among groups. Core mass-averaged diameters of groups L and H were larger than the control groups (LC and HC). Fibril diameter of group LH (combined treatment) was even larger and approaching that of the intact MCL.

CONCLUSION

Combined therapeutic laser and herbal treatment hastened collagen fibril maturation in MCL repair.

In vivo local administration of osteogenic protein-1 increases structural properties of the overstretched anterior cruciate ligament with partial midsubstance laceration

We report the effects of local administration of osteogenic protein-1 on the biomechanical properties of the overstretched anterior cruciate ligament in an animal model. An injury in the anterior cruciate ligament was created in 45 rabbits. They were divided into three equal groups. In group 1, no treatment was applied, in group II, phosphate-buffered saline was applied around the injured ligament, and in group III, 12.5 μg of osteogenic protein-1 mixed with phosphate-buffered saline was applied around the injured ligament. A control group of 15 rabbits was assembled from randomly-selected injured knees from among the first three groups. Each rabbit was killed at 12 weeks.

The maximum load and stiffness of the anterior cruciate ligament was found to be significantly greater in group III than either group 1 (p = 0.002, p = 0.014) or group II (p = 0.032, p = 0.025). The tensile strength and the tangent modulus of fascicles from the ligament were also significantly greater in group III than either group I (p = 0.002, p = 0.0174) or II (p = 0.005, p = 0.022).

The application of osteogenic protein-1 enhanced the healing in the injured anterior cruciate ligament, but compared with the control group the treated ligament remained lengthened. The administration of osteogenic protein-1 may have a therapeutic role in treating the overstretched anterior cruciate ligament.

The effect of therapeutic ultrasound intensity on the ultrastructural morphology of tendon repair

This study evaluated the effects of ultrasound intensity on the ultrastructural morphology of Achilles tendon healing. Twenty Sprague-Dawley rats with surgically hemi-transected Achilles tendons were randomly assigned into four groups of 0, 0.5, 1.2 and 2 W/cm(2) for ultrasound treatment, with five rats in each group. The treatments were administered with 1 MHz continuous ultrasound daily starting from day 5 after injury. On day 30, ultrathin slides of the Achilles tendons were prepared and examined with transmission electron microscopy. Results showed that the mean collagen fibril size of all treatment groups was higher than the control (p < 0.05). There was no significant difference in the collagen fibril size among the treatment groups. These findings suggest that therapeutic ultrasound can enhance the maturation of collagen fibrils of repairing tendons, and this was not dependent on the intensity of ultrasound applied.

Effects of low-voltage microamperage stimulation on tendon healing in rats

STUDY DESIGN

Randomized controlled prospective experimental study.

OBJECTIVES

To examine the effects of transcutaneous low-voltage microamperage stimulation (LVMAS) on the mechanical strength of Achilles tendon repair in rats at 4 weeks after injury.

BACKGROUND

Understanding the effect of LVMAS on the healing of injured tendons is hampered by the lack of related experimental studies, especially from the aspect of biomechanical outcome measures.

METHODS AND MEASURES

Fourteen 3-month-old male Sprague-Dawley rats received surgical transection to the medial portion of their right Achilles tendon. The rats were divided into a LVMAS group (n = 7) and control group (n = 7). From day 6 postsurgery onwards, the LVMAS group received daily treatment of transcutaneous LVMAS (2.5 V, 100 microA/cm2, 10 pulses per second, positive current) for a total of 22 sessions, while the control group received placebo LVMAS by the same investigator during that period. On day 31, the Achilles tendons were harvested for biomechanical testing for load relaxation, stiffness, and ultimate tensile strength along the longitudinal direction.

RESULTS

The normalized Achilles tendon ultimate tensile strength of the LVMAS group (mean +/- SD, 110.5% +/- 25.0%) was higher than that of the control group (75.3% +/- 20.8%) (P = .014), but no significant difference was found in normalized stiffness and load relaxation between the 2 groups (P = .239 and .350, respectively).

CONCLUSION

The results of this study suggest that the administration of transcutaneous LVMAS could improve healing and consequently the tensile strength of partially transected Achilles tendons of rats at 4 weeks after injury.

The central ACL defect as a model for failure of intra-articular healing

Intra-articular soft tissues, such as the anterior cruciate ligament (ACL), fail to heal in contrast to the extra-articular medial collateral ligament (MCL), which undergoes classic healing. The goal of this study was to validate a model for failure of intra-articular healing that could be used in the future to test new repair strategies. We conducted a two-part experiment, the first part ex vivo, and the second in vivo. Our initial ex vivo experiments were used to determine the optimal width of the central defect in the canine ACL that would produce reproducible structural properties at time zero. The second experimental series used this optimal scalpel blade width to create a central defect in the canine ACL followed by measurement of structural properties in the ACL after either a 3- or 6-week in vivo healing period. A 3.5-mm beaver blade resulted in a maximum tolerated load of 56.8 +/- 4.7% (mean +/- SEM) of control at time zero. After the 3- and 6-week in vivo healing periods, the maximum load was 74.6 +/- 5.3 at 3 weeks and 64.9 +/- 3.8% at 6 weeks compared to control. Thus, biomechanical parameters tested at 6 weeks after creation of a defect showed no significant gains from defects tested immediately after the creation of injury. The centrally placed ACL defect in this canine model demonstrates failure to mechanically heal, which should prove suitable for future in vivo evaluation of the biomechanical and histological response to tissue engineering repair strategies for intra-articular soft tissues.

Pulsed ultrasound treatment accelerates the repair of Achilles tendon rupture in rats

A rat tenotomy model was used to investigate the effect of combined conservative management and pulsed ultrasound (PUS) on the repair of tenotomized Achilles tendon. Hemitenotomy of right medial Achilles tendon was performed in 48 rats without suture, and patella tenotomy was performed to mimic immobilization and limb disuse of an injured limb. PUS and sham PUS were applied to the healing wound for the treatment group and control group for 5 min, 3 times per week for 2 or 4 weeks, respectively. Tensile tests showed that the ultimate tensile strength (UTS) and stiffness of the repaired tendon in the treatment group at 2 weeks reached 48.92+/-8.39% and 62.48+/-32.46% of the contralateral normal tendon strength, which were significantly higher than those of the control group (UTS, 30.36+/-15.46%; stiffness, 33.90+/-17.59; p<0.05). At 4 weeks, UTS increased to 77.09+/-15.31% and stiffness to 92.48+/-31.12% in the treatment group, significantly higher than those in the control group (UTS, 54.33+/-18.40%, p<0.01; stiffness, 65.02+/-25.48%, p<0.05). Light microscopy revealed more regular, denser, and better aligned collagen fibers in the healing scar of the PUS-treated healing tendons. The findings suggested that PUS were able to accelerate the healing of the ruptured tendons.

Thermal modification of partial tears of the anterior cruciate ligament

PURPOSE

Partial tears of the anterior cruciate ligament (ACL) are common, representing 10% to 28% of all ACL tears. Untreated partial tears of the ACL may go on to complete rupture in up to 42% of cases, and as few as 30% of patients return to their preinjury activity level. The purpose of this study was to evaluate the effectiveness of thermal modification for the treatment of partial tears of the ACL.

TYPE OF STUDY

A prospective, nonrandomized consecutive case series.

METHODS

Thirteen patients with a partial tear of a native ACL were treated with thermal modification of the ACL. All patients had a preoperative office examination significant for an end-point to Lachman examination and pivot-glide. All patients had bilateral preoperative KT-1000 measurements. All tears were confirmed by arthroscopy to constitute a 50% or less loss of structural integrity of the ligament. The ACL underwent thermal modification using the Oratec thermal probe (Oratec Interventions, Menlo Park, CA), and was examined by intraoperative KT-1000 testing. Patients were evaluated postoperatively at 6 weeks, and at 3, 6, 12, and 24 months by office examination and functional outcome scoring.

RESULTS

KT-1000 arthrometer testing revealed a mean side-to-side difference of 4.35 mm preoperatively (SD = 1.1 mm). At the most recent follow-up, averaging 23 months (range, 18 to 28 months), 10 patients had a negative Lachman examination and no pivot-shift. Two patients had persistent grade II Lachman and complaints of giving way 3 months postoperative. Both patients underwent ACL reconstruction. One patient was lost to follow-up. Of the remaining 10 patients, all patients achieved full extension, and the average flexion range of motion was 131 degrees (SD = 5.6). Compared with the preoperative KT-1000 arthrometer testing, the most recent evaluation revealed a decrease in mean side-to-side difference to 1.9 mm (SD = 1.5 mm). At most recent follow-up, the mean Lysholm score was 96.3 (SD = 4.4), the mean Tegner score was 6.1 (SD = 1.2), and the mean Cincinnati score was 94 (SD = 3.0).

CONCLUSIONS

With cautious application, thermal modification may be a viable treatment option for partial tears of the ACL in a select subset of patients. Further investigation is necessary to determine the long-term effectiveness of this procedure.

LEVEL OF EVIDENCE

Level IV, Therapeutic Case Series Study (no or historical control group).

Running exercises improve the strength of a partially ruptured Achilles tendon

OBJECTIVES

To examine the effects of running and swimming exercises on the functional performance and mechanical strength of a recovering Achilles tendon.

METHODS

30 Sprague-Dawley rats had surgical transection of their right medial Achilles tendon. The rats were divided into running (n = 11), swimming (n = 10), and control (n = 9) groups. The running and swimming groups were given daily exercise training, starting from the fifth day after the injury; the control group did not exercise throughout the period of the experiment. An Achilles functional index (AFI) was recorded before the operation and on the third, 10th, and 30th days after the operation. On the 30th day, the rats were killed and their Achilles tendons harvested for biomechanical testing of load relaxation properties, stiffness, and ultimate tensile strength (UTS). The AFI data were analysed by two way analysis of variance; load relaxation, stiffness, and UTS data were analysed by multivariate analysis, with alpha at 0.05.

RESULTS

The UTS of the running group was higher than in the control group (p = 0.015), while there was no significant difference between the swimming and control groups (p = 0.228). Differences in stiffness and load relaxation were non-significant (p = 0.823 and 0.633, respectively). The AFI results did not differ among the three groups (p = 0.242).

CONCLUSIONS

Running exercises can improve the strength of partially ruptured Achilles tendons at 30 days after injury.

Effects of administration of exogenous growth factors on biomechanical properties of the elongation-type anterior cruciate ligament injury with partial laceration

BACKGROUND

No studies have been conducted to clarify the in vivo effect of growth factor application on healing in the injured anterior cruciate ligament.

HYPOTHESIS

Administration of exogenous growth factors significantly increases the structural properties of the injured anterior cruciate ligament.

STUDY DESIGN

Controlled laboratory study.

METHODS

Thirty-six rabbits were randomly divided into 4 groups of 9 animals each after an overstretched injury was made in the right anterior cruciate ligament. In group 1, no treatment was applied around the injured anterior cruciate ligament. In group 2, 0.2 mL fibrin sealant was applied around it. In group 3, 4 ng transforming growth factor-beta1 mixed with 0.2 mL fibrin sealant was applied. In group 4, 20 microg platelet-derived growth factor-BB mixed with 0.2 mL fibrin sealant was applied. Each rabbit was sacrificed at 12 weeks after the surgery. In addition, 9 knees randomly harvested from all the left knees were used to obtain normal control data. The femur-anterior cruciate ligament-tibia complex specimens were biomechanically and histologically evaluated.

RESULTS

Concerning the maximum load and the stiffness, group 3 was significantly greater than groups 1 and 2, whereas there were no significant differences among groups 1, 2, and 4. Groups 1, 2, 3, and 4 were significantly lower than the control group.

CONCLUSIONS

The application of 4 ng transforming growth factor-beta1 significantly enhances healing in the injured anterior cruciate ligament.

CLINICAL RELEVANCE

Administration of certain growth factors is of value to be studied as one of the future therapeutic options for the overstretched anterior cruciate ligament injury.

Combined treatment of therapeutic laser and herbal application improves the strength of repairing ligament

The present study investigated the effects of combined therapeutic laser and herbal medication protocols on injured medial collateral ligaments (MCLs) of rat knees. Fully 36 rats were evenly divided into 9 groups. Right MCLs of groups 1 to 6 and 8 were transected, while that of groups 7 and 9 remained intact. After surgery, group 1 was treated with 1 session of high-dosed laser; group 2 with 9 sessions of low-dosed laser; group 3 with an herbal plaster; groups 4 and 5 received combined treatments of groups 1 and ss and 2, and 3 respectively; groups 6 and 7 received only bandaging; groups 8 and 9 received placebo laser and no treatment, respectively. All MCLs were subjected to biomechanical testing at 3 weeks postsurgery. Results revealed significant differences among groups in ultimate tensile strength (UTS) and stiffness (p < 0.01). Combination of multiple low-dosed laser treatment with herbal treatment (group 5) resulted in higher UTS than either no treatment (groups 6 and 8), single high-dosed laser treatment (group 1), multiple low-dosed laser treatment (group 2), or herbal treatment (group 2) alone. We concluded that combined applications of laser and herb can enhance further biomechanical properties of repairing rat MCLs than separate applications at 3 weeks postinjury.

Herbal remedies improve the strength of repairing ligament in a rat model

Herbal remedies have been reported to be effective in controlling inflammation for acute soft tissue injuries. There exist, however, no reports of their effects on collagen production and remodeling; thus mechanical strength studies of the tissues have not been reported. This study tested the effects of a herbal remedy on the strength of healing medial collateral ligaments (MCL) in rats. Sixteen rats receiving surgical transection to their right MCLs and eight receiving sham operation were tested. Eight of the MCL-injured animals were treated with an adhesive herbal plaster application to their right knees, while the other eight in the MCL injured group and the sham group were treated with plain adhesive plaster to their right knees. The MCLs were harvested and tested at either 3 or 6 weeks post-operation. The ultimate tensile strength (UTS) and stiffness normalized to the uninjured side of each animal of the herb and sham groups were significantly larger than those of the control at both 3 and 6 weeks (p = 0.001). No significant difference was found in stiffness between the herb and sham groups (p > 0.05). We concluded that the herbal remedy improves the UTS and stiffness of repairing MCLs at 3 and 6 weeks after injury.

Comparison of therapeutic ultrasound and exercises for augmenting tendon healing in rats

We compared therapeutic ultrasound (US) and exercises on Achilles tendon healing in 49 mature male rats. The medial Achilles tendon of the right leg was transected and the rats were divided into five groups: 1. control (n = 9), 2. 1 W/cm(2) US (n = 9), 3. 2 W/cm US (n = 10), 4. running (n = 11) and 5. swimming (n = 10). All animals were treated daily, starting from postsurgical day 5, according to their group assignment, except for group 1 control. Achilles functional index (AFI) was recorded pre- and postoperatively. On day 30, the Achilles tendons were biomechanically tested. Results revealed that groups 3 and 4 had higher tensile strength than the controls (p = 0.037 and 0.034), but groups 2 and 5 were not different from the controls. No significant difference in stiffness (p = 0.21) or AFI (p = 0.22) was found. These findings suggest that therapeutic US treatment at 2 W/cm(2) and running exercise improved the strength of repairing Achilles tendon.

Ultrastructural comparison of medial collateral ligament repair after single or multiple applications of GaAlAs laser in rats

BACKGROUND AND OBJECTIVES

To examine single versus multiple applications of a gallium aluminum arsenide (GaAlAs) laser on the ultrastructural morphology of surgically injured medial collateral ligaments (MCLs) in rats.

STUDY DESIGN/MATERIALS AND METHODS

Sixteen rats were studied with 12 receiving right MCL transection and 4 receiving sham injury. Group 1 (n = 4) received one session of laser (31.6 J/cm(2)) immediately after injury. Group 2 (n = 4) received 9 doses of transcutaneous laser (3.5 J/cm(2)). The controls (Group 3, n = 4) received one session of placebo laser, while the sham Group 4 (n = 4) received no treatment. Ultrastructural analyses were done with electron microscopy at 3 weeks.

RESULTS

The mass-averaged diameters of collagen fibril in the core and periphery of MCLs treated with multiple laser were larger than the control and those with single laser treatment (P < 0.05). However, the sham injured group had larger fibrils than all other groups (P < 0.05).

CONCLUSIONS

The repairing MCLs had smaller collagen fibrils than the sham injured ligaments. Multiple laser treatments enhanced the collagen growth in the repairing MCLs at 3 weeks after injury, which are superior to a single treatment with similar dosage.

Comparison of single and multiple applications of GaAlAs laser on rat medial collateral ligament repair

BACKGROUND AND OBJECTIVES

To examine single versus multiple applications of the gallium aluminum arsenide (GaAlAs) laser on the healing of surgically injured medial collateral ligaments (MCLs) in rats.

STUDY DESIGN/MATERIALS AND METHODS

Sixteen rats were studied, with 12 receiving surgical transection to their right MCL and 4 receiving a sham injury. Group 1 (n = 4) received a single dose of GaAlAs laser therapy (wavelength 660 nm, average power 8.8 mW, pulse 10 kHz, dosage 31.6 J/cm(2)) directly to their MCL during surgery. Group 2 (n = 4) received 9 doses of GaAlAs laser therapy applied transcutaneously on alternate days (wavelength 660 nm, average power 8.8 mW, pulse 10 kHz, dosage 3.5 J/cm(2)). The controls (Group 3, n = 4) received one session of placebo laser at the time of surgery, with the laser equipment shut down, while the sham injured Group 4 (n = 4) received no treatment. Biomechanical tests for structural stiffness, ultimate tensile strength (UTS), and load-relaxation were done at 3 weeks after injury. The stiffness and UTS data were normalized by expressing as a percentage of the left side of each animal before statistical analysis.

RESULTS

The load-relaxation data did not show any differences between the groups (P = 0.18). The normalized stiffness levels of Groups 2 (81.08+/-11.28%) and 4 (92.66+/-13.19%) were significantly higher (P = 0.025) than that of the control Group 3 (58.99+/-15.91%). The normalized UTS of Groups 2 (81.38+/-5.68%) and 4 (90.18+/-8.82%) were also significantly higher (P = 0.012) than that of the control (64.49+/-9.26%). Although, Group 1 had higher mean stiffness and UTS values than the control, no statistically significant difference was found between these two groups.

CONCLUSIONS

Multiple laser therapy improves the normalized strength and stiffness of repairing rat MCLs at 3 weeks after injury. The multiple treatments seem to be superior to a single treatment when the cumulative dosages are comparable between the two modes of application.

The immediate effects of tension of counterforce forearm brace on neuromuscular performance of wrist extensor muscles in subjects with lateral humeral epicondylosis

STUDY DESIGN

Within-subject repeated-measures study.

OBJECTIVES

To examine the immediate effects of counterforce forearm brace on isokinetic strenght stretch reflex, passive stretching pain threshold of the wrist extensors, and proprioception of the wrist in subjects with lateral humeral epicondylosis for different strap tensions of a forearm brace.

BACKGROUND

Counterforce forearm bracing has been used for treating lateral humeral epicondylosis, but the effect of brace tension has not been well reported.

METHODS AND MEASURES

Fifteen subjects diagnosed with lateral humeral epicondylosis on their dominant arm were tested under 4 randomized conditions: (1) no brace, (2) brace with minimal tension, (3) brace with 25-N tension, and (4) brace with 50-N tension. The tests included isokinetic wrist extensors strength, passive stretching force in wrist flexion to elicit pain in the wrist extensors, wrist proprioception, and stretch reflex latency of the extensor carpi ulnari. A repeated-measures MANOVA was used to analyze the data and significant results were further analyzed with post hoc linear contrasts (alpha = .05).

RESULTS

Among the 4 conditions, significant differences were found in wrist proprioception P = .032) and pain threshold to passive stretching of the wrist extensors (P = .05), but were not found in wrist extension isokinetic strength and stretch reflex latency of the extensor carpi ulnaris.

CONCLUSION

A forearm counterforce brace, as applied in this study, affects wrist joint proprioception and increases the pain threshold to passive stretching of the wrist extensors in subjects with lateral humeral epicondylosis, but it has no effect on wrist extensor strength and stretch reflex latency of the extensor carpi ulnaris.

Biomechanical evaluation of a newly devised model for the elongation-type anterior cruciate ligament injury with partial laceration and permanent elongation

OBJECTIVE

To biomechanically evaluate a newly devised model for the elongation-type anterior cruciate ligament injury with partial laceration and permanent elongation.

DESIGN

Thirty-six rabbits were randomly divided into 4 groups of 9 animals each, after a quantitative injury was given to the right anterior cruciate ligament. The 4 groups were sacrificed at 0, 6, 12, and 24 weeks after surgery, respectively. Biomechanical and histological evaluations were performed at each period.

BACKGROUND

No adequate animal models have been established for the elongation-type anterior cruciate ligament injury in which the mid-substance is permanently elongated with partial laceration.

METHODS

The anteromedial and posterolateral half of the anterior cruciate ligament was transected at the proximal and distal one-third levels, respectively. Then, the anterior cruciate ligament was stretched by applying an anterior drawer force to the tibia at 90 degrees of knee flexion.

RESULTS

The treatment significantly increased the anterior translation of the knee into approximately 150-250% at each period after surgery. The maximum load and the stiffness of the femur-anterior cruciate ligament-tibia complex significantly decreased to 30% or less immediately after surgery, and then gradually increased to 50% at 12 weeks.

CONCLUSIONS

In this model, this quantitative treatment created serious injuries with partial laceration and permanent elongation in the anterior cruciate ligament to similar degrees. Also, incomplete tissue healing occurred in the anterior cruciate ligament to similar degrees after the treatment.

RELEVANCE

This model will be useful to study new therapeutic methods for the elongation-type anterior cruciate ligament injury.

Therapeutic ultrasound improves strength of achilles tendon repair in rats

The purpose of this study was to evaluate the effects of therapeutic ultrasound on structural properties and functional performance of Achilles tendon healing. Thirty Sprague-Dawley rats with surgical hemitransected Achilles tendon were studied. Ten were treated daily with 1 MHz continuous ultrasound at 1.0 W/cm2 for 4 min, 11 at 2.0 W/cm2 for 4 min and nine served as control without treatment. Achilles functional index (AFI) was recorded preoperatively and on postoperative days 3, 10 and 30. On day 30, the rats were sacrificed and Achilles tendons were tested for load-relaxation, stiffness and ultimate tensile strength (UTS). Results showed that UTS of both low-dose (p=0.023) and high-dose (p=0.002) groups was significantly greater than in controls. No significant differences in AFI (p=0.179), load-relaxation (p=0.205) and stiffness (p=0.842) were found among groups. These findings suggested that both low- and high-dose therapeutic ultrasound accelerate the healing process of ruptured tendon.

Therapeutic low energy laser improves the mechanical strength of repairing medial collateral ligament

BACKGROUND AND OBJECTIVES

Low energy laser therapy has been shown to enhance collagen production but its effect on tissue strength is not well reported. We tested the effects of therapeutic laser on the strength of healing medial collateral ligaments (MCLs) in rats.

STUDY DESIGN/MATERIALS AND METHODS

Twenty-four rats received surgical transection to their right MCL and eight received sham operation. After surgery, 16 received a single dose of gallium aluminum arsenide laser to their transected MCL for 7.5 minutes (n = 8) or 15 minutes (n = 8) and eight served as control with placebo laser, while the sham group didn't receive any treatment. The MCLs were biomechanically tested at either 3 or 6 weeks post-operation.

RESULTS

The normalized ultimate tensile strength (UTS) and stiffness of laser and sham groups were larger than control (P < 0.001). The UTS of laser and sham groups were comparable. Laser and sham groups had improved in stiffness from 3 to 6 weeks (P < 0.001).

CONCLUSIONS

A single dose of low energy laser therapy improves the UTS and stiffness of repairing MCL at 3 and 6 weeks after injury.

Partial tears of the anterior cruciate ligament in children and adolescents

BACKGROUND

The functional outcome after partial anterior cruciate ligament tears in children and adolescents treated without reconstruction has not been established.

HYPOTHESIS

Nonreconstructive management of partial anterior cruciate ligament tears can be effective in certain pediatric patients.

STUDY DESIGN

Prospective cohort study.

METHODS

We studied 45 skeletally mature and immature patients 17 years of age or less who had an acute hemarthrosis, magnetic resonance imaging signal changes, grade A or B Lachman and pivot shift result, and an arthroscopically documented partial anterior cruciate ligament tears. All patients were treated without reconstruction, underwent a structured rehabilitation program, and were followed up for a minimum of 2 years.

RESULTS

Fourteen patients (31%) underwent subsequent reconstruction. Significant associations with subsequent reconstruction included tears that were greater than 50%, predominantly posterolateral tears, a grade B pivot shift test result, and older chronologic and skeletal age. Among patients who did not require reconstruction, those with tears that were greater than 50% or predominantly posterolateral had significantly lower Lysholm, satisfaction, and Cincinnati Knee Scale scores.

CONCLUSIONS

Nonreconstructive management is recommended for partial anterior cruciate ligament tears in children and adolescents 14 years of skeletal age or younger with normal or near-normal Lachman and pivot shift results. Reconstruction is recommended in older athletes or in those with greater than 50% or predominantly posterolateral tears.

Functional assessment and tissue response of short- and long-term absorbable surgical meshes

Within the last few years meshes have become essential for the temporary closure of the abdominal cavity to avoid the development of an intra-abdominal compartment syndrome. The interposition of a mesh as an inlay reduces the intra-abdominal pressure and improves markedly the blood circulation, particularly for the intestines and kidneys. Whereas non-absorbable meshes usually tend to produce fistulas in direct contact to the bowels, the interposition of short-term absorbable meshes result in large incisional hernias in almost all cases. In the following study we investigated the functional and histological consequences of a short-term absorbable mesh (polyglactin 910, Vicryl, loss of 50% of its mechanical stability within 3 weeks) and a long-term absorbable mesh (polylactide, LTS, preserved >50% of its mechanical stability for over 1 year). The mesh-modifications were both tested with the aid of three-dimensional stereography, tensiometry, light- (LM) and transmission electron microscopy (TEM) as well as morphometry after implantation intervals of 3, 7, 14, 21, 45, 90, 135 and 180 days in a standardised rat model. The PG-mesh initially revealed a pronounced inflammatory reaction and a significantly increased formation of connective tissue. The extensive arrangement of connective tissue in the interface mesh/recipient tissues correlated to an increased stiffness of the abdominal wall compared to the sham-group. However, a loss of mechanical stability and an increase of elasticity could be detected after 3 weeks of implantation which may be explained by the rapid absorption of the mesh material. In contrast to PG, the LTS-mesh indicated a decreased but persisting inflammatory reaction in the interface mesh-fibres/recipient tissues and a significantly reduced induction of connective tissue. Although, the formation of scar-tissue was diminished compared to PG the LTS-mesh preserved its mechanical stability after 180 days. The results indicate that the frequent development of incisional hernias with short-term absorbable meshes (PG) might be due to the decreased mechanical stability and dilatation of the newly formed connective tissue after 2-3 weeks. Moreover, extensive scar tissue development may promote adhesion formation. The implantation of the long-term absorbable LTS-mesh seems to be favourable with respect to its long-term mechanical stability and the decreased connective tissue formation.

Interaction between the ACL graft and MCL in a combined ACL+MCL knee injury using a goat model

The optimal treatment for the MCL in the combined ACL and MCL-injured knee is still controversial. Therefore, we designed this study to examine the mechanical interaction between the ACL graft and the MCL in a goat model using a robotic/universal force-moment sensor testing system. The kinematics of intact, ACL-deficient, ACL-reconstructed, and ACL-reconstructed/ MCL-deficient knees, as well as the in situ forces in the ACL, ACL graft, and MCL were determined in response to two external loading conditions: 1) anterior tibial load of 67 N and 2) valgus moment of 5 N-m. With an anterior tibial load, anterior tibial translation in the ACL-deficient knee significantly increased from 2.0 and 2.2 mm to 15.7 and 18.1 mm at 30 degrees and 60 degrees of knee flexion, respectively. The in situ forces in the MCL also increased from 8 to 27 N at 60 degrees of knee flexion. ACL reconstruction reduced the anterior tibial translation to within 2 mm of the intact knee and significantly reduced the in situ force in the MCL to 17 N. However, in response to a valgus moment, the in situ forces in the ACL graft increased significantly by 34 N after transecting the MCL. These findings show that ACL deficiency can increase the in situ forces in the MCL while ACL reconstruction can reduce the in situ forces in the MCL in response to an anterior tibial load. On the other hand, the ACL graft is subjected to significantly higher in situ forces with MCL deficiency during an applied valgus moment. Therefore, the ACL-reconstructed knee with a combined ACL and MCL injury should be protected from high valgus moments during early healing to avoid excessive loading on the graft.