The patient is placed supine and given either general or spinal anesthesia. After sterile draping and preparation, a complete knee examination is performed. Examination tests of knee stability are performed, followed by Rolimeter testing (Don Joy). Routine arthroscopic examination of the knee is performed, carefully noting cruciate ligament integrity. Partial tearing of the ACL or PCL is confirmed by probing the individual bundles at varying flexion angles, and with the knee in a figure-of-4 position. Lachman and jerk tests are performed under direct visualization of the ligaments to supplement the examination of ligamentous injury. After identification of the injured ligament fibers, polydioxanone suture no. 1 (Ethicon, Piscataway, New Jersey) is then passed through and around the residual distal and proximal fibers using a standard clever hook, and tied using a Duncan loop to reappose the torn ligament (Fig. 24.3a). The role of these sutures is to reapproximate the torn fibers in order to minimize gapping between the residual tissues, thereby recreating continuity of the ligament. Subsequent healing is promoted by adjacent marrow stimulation within the notch to facilitate the release of PSCs (Fig. 24.3b). Microfracture perforations, 1.5 mm in diameter, 3–4 mm apart, and 3 mm deep, are made around the anatomic femoral insertion of the injured intra-articular ligament. Great care is taken to avoid damaging the preserved ligamentous insertion. Release of marrow elements from the microfracture site is confirmed under direct visualization. In cases where the ACL fibers appear stretched but not interrupted, we perform marrow stimulation without ligament suturing.

Platelet-rich plasma is then prepared using a commercially available system. The PRP is subsequently activated with batroxobin enzyme (Plateltex^® act-S.R.O., Bratislava, SK) to produce a sticky PRP gel, which is then injected at the repaired site to biologically augment ligamentous healing. Recently, biologic augmentation of ligament repair has extended to the use of bone marrow aspirate concentrate (BMAC), which provides cellular augmentation, in addition to platelet-derived growth factors. As with PRP, the BMAC is activated using batroxobin to create an activated clot, which is then applied to the site of ligament repair under dry arthroscopy.

In our study period from 2004 to 2009 [33], there were 26 athletes included in the analysis with incomplete tears of the ACL who underwent primary repair, followed by bone marrow stimulation about the ACL femoral attachment site and biologic augmentation. All patients participated in a specific rehabilitation program and were evaluated pre- and postoperatively by Marx, Noyes, Tegner, Single Assessment Numeric Evaluation, Lysholm, and International Knee Documentation Committee scores. Anterior tibial translation was measured using a Rolimeter under anesthesia, and at final follow-up. After a mean follow-up period of 25.3 months, all patients had excellent functional outcomes and had returned to sporting activities. Second look arthroscopy in six patients revealed that the repaired ACL bundles had excellent vascularity, minimal fibrous tissue, and good stability on probing. Partial PCL tears have also been treated with this technique at our institution, and patient clinical outcomes are currently undergoing analysis. In cases of combined ligamentous injury where there is low- to moderate-grade injury to the medial or lateral collateral ligament, the injured collateral ligament is typically treated with a biologic injection consisting of PRP or BMAC (Fig. 24.4). Isolated MCL and LCL tears that do not require surgical intervention are often treated with PRP injection in and around the injured ligament at our outpatient clinics (Figs. 24.5 and 24.6).

The operative knee is positioned into a brace, and partial weight bearing is allowed with crutches for 3 weeks. Continuous passive motion (CPM) is used initially at 20–60° of knee flexion, and is increased gradually until 90° is achieved by 2 weeks postoperatively, after which CPM is discontinued. At least 120° of flexion is expected by 6 weeks. Proprioceptive and strength training progresses systematically, with running activities commencing at 3 months. Return to high contact sports is delayed for a minimum of 4–5 months postoperatively.

Growth factors have been shown to enhance cellular proliferation and migration, as well as increase collagen production, according to a number of in vitro studies. Various bioactive molecules are involved in orchestrating the cellular repair response after tendon repair [36]. Numerous growth factors are markedly upregulated following tendon injury and are active at multiple stages of the healing process, including insulin-like growth factor-1 (IGF-1), transforming growth factor beta (TGF-β), basic fibroblast growth factor (bFGF), platelet-derived growth factor (PDGF), vascular endothelial growth factor (VEGF), bone morphogenic protein (BMP), and connective tissue growth factor (CTGF) [37–40]. IGF-1 is an important mediator during the inflammatory and proliferative phase of tendon healing, while PDGF, FGF, BMP, and TGF-β have also been shown to play important roles in ligamentous healing.

Kobayashi et al. have reported improved healing and vascularity following instillation of FGF after canine ACL injury [41]. Aspenberg et al. demonstrated improved healing in cases of Achilles tendon injury treated with GDF 5 (BMP 14) [42]. These growth factors have been used in conjunction with synthetic scaffolds with the goal of enhancing ligament repair. Chen et al. examined the use of BMP 2 with hydrogel and periosteum to stimulate tendon-bone healing in a model of ACL reconstruction, and reported that PPC-BMP-hydrogel composite is an effective inducer of healing, being capable of acting as a matrix for encapsulation of cell and growth factors [43].

PRP has been defined as a volume of plasma fraction isolated from autologous blood with a platelet concentration above the baseline level (200,000 platelets/μL). Platelets contain many important bioactive proteins and growth factors. These factors regulate key processes in tissue repair, including cellular chemotaxis, migration, proliferation, differentiation, and extracellular matrix synthesis. The rationale for PRP use is to stimulate and augment the natural healing cascade by providing a “supra-physiologic” release of platelet-derived factors directly at the site of injury.

Autologous PRP can be obtained from simple venous blood extraction with a commercially available kit. After collection, the blood undergoes a centrifugation process to isolate PRP. For PRP gel preparations, platelets are typically activated by thrombin (autologous or animal derived), calcium chloride, or a procoagulant enzyme, such as batroxobin, which works as a fibrinogen-cleaving enzyme that induces rapid fibrin clot formation. When PRP isolates are injected into a site of tissue injury, platelets are activated by endogenous thrombin and/or intra-articular collagen. Depending on the preparation method, PRP can be categorized as leucocyte-rich PRP (L-PRP), leucocyte-poor PRP (LP-PRP), or platelet-poor plasma (PPP) [44]. The constituents of PRP preparations may vary, depending on which system is used to process the autologous blood. Our institution prefers to use PRP preparations rich in the growth factors PDGF, TGF-β, and IGF-1, which have been shown in vitro to be particularly effective in encouraging biologic healing processes (Figs. 24.7 and 24.8).

Some researchers have questioned the beneficial effects of isolated PRP use in tissue healing. Murray et al. contested the beneficial role of PRP in ACL healing following the outcomes demonstrated in skeletally immature pigs that were treated with ACL repair in conjunction with PRP injection [45]. The addition of PRP to the sutured ACL repairs did not improve AP knee laxity, maximum tensile load, or linear stiffness of the ACL after 14 weeks in vivo, compared to a sample that underwent ACL repair without the addition of PRP. In an alternate porcine model of ACL repair, however, Murray et al. reported that the use of collagen-platelet composites did have beneficial effects on sutured ACL repair [46].