The range of allograft products for spinal fusion has been extended with the development of cellular bone matrices (CBMs). Most of these combine demineralized bone with viable cancellous bone prepared in a manner that retains cells with differentiation potential. The purpose of this study was to compare commercially-available human CBMs in the athymic rat model of posterolateral spinal fusion. The products compared were Trinity ELITE® (TEL, OrthoFix), ViviGen (VIV, DePuy Synthes), Cellentra (CEL, Zimmer Biomet), Osteocel® Pro (OCP, NuVasive), Bio4 (BIO, Stryker) and map3 (MAP, RTI Surgical). Bone from the ilia of syngeneic rats was used as a control to approximate the human gold standard.

All implants were stored, thawed, and prepared per manufacturer's instructions and all implantations occurred within the manufacturer's time allowance for use after preparation. In total, fifteen 9–10 week old male rats were implanted per implant type, with three different lots of each implant used per five rats to account for lot-to-lot variability. Under anesthesia, a posterior midline longitudinal skin and subcutaneous incision was made, followed by bilateral longitudinal paraspinal myofascial incisions to expose the transverse processes at the L4–5 level. Implants (0.3 cc of allograft or freshly harvested syngeneic iliac bone graft) were placed bilaterally. Surgeons were blinded as to CBM implant type. Incisions were closed with sutures and in vivo microCT scans performed within 48 hours of surgery. A second microCT scan was taken at euthanasia, six weeks after surgery, and the lumbar spines harvested. Fusion was evaluated by manual palpation by three independent, blinded reviewers. MicroCT analysis was performed by an independent CRO (ImageIQ, Cleveland OH). Anonymity of implant type was rigorously kept to avoid bias.

By manual palpation, 5/15 (33%) spines of the syngeneic bone group were fused at 6 weeks. The TEL (8/15, 53%) and CEL (11/15, 73%) groups were not significantly different from each other but were from all other CBM groups. Only 2/15 (13%) of VIV-implanted spines fused and none (0/15, 0%) of the OCP, BIO and MAP CBMs produced stable fusion. The mineralized cancellous bone component of the allografts confounded radiographic analysis but microCT analysis indicated bone volume increased over six weeks for all groups except the syngeneic bone (−4.3%). TEL (+65%) and CEL (+73%) were not different from each other but were significantly increased over all other groups (VIV 29%, OCP 37%, BIO 19%, and MAP 45%, respectively).

CBMs have distinct formulations and are likely processed differently. The claimed live cell and stem cell contents differ between products. Additionally, map3 has cells added at the time of surgery, whereas the other CBMs are processed to retain matrix-adherent cells. Given the wide range of formulations, differences in performance were not surprising, and Trinity ELITE and Cellentra did significantly better than other implants at both forming new bone and achieving fusion. The other CBMs did not have greater bone formation than the control and were very poor at forming a solid fusion. These findings suggest more careful consideration of these allograft products is needed at the clinical level.

Dexmedetomidine, an alpha 2 agonist, has been approved for providing sedation in the intensive care unit. Along with sedative properties, it has analgesic activity through its highly selective action on alpha 2 receptors. Recent studies have examined the use of dexmedetomidine as an adjuvant to prolong the duration of peripheral nerve blocks. Studies showing effectiveness of dexmedetomidine for adductor canal block in knee surgery are small. Also, its effectiveness has not been compared to Epinephrine which is a strong alpha and beta receptor agonist. In a previous study, we showed that motor sparing knee blocks significantly increased the duration of analgesia compared with periarticular knee infiltration using local anesthetic mixture containing Epinephrine following total knee arthroplasty (TKA). In this study, we compared two local anesthetic mixtures: one containing Dexmedetomidine and the other Epinephrine for prolongation of motor sparing knee block in primary TKA patients.

After local ethics board approval and gaining Notice of Compliance (NOC) from Health Canada for use of Dexmedetomidine perineurally, 70 patients between the ages 18 – 95 of ASA class I to III undergoing unilateral primary total knee arthroplasty were enrolled. Motor sparing knee block − 1) Adductor canal continuous catheter 2) Single shot Lateral Femoral Cutaneous Nerve block 3) Single shot posterior knee infiltration was performed in all patients using 60 ml mixture of 0.5% Ropivacaine, 10 mg Morphine, 30 mg Ketorolac. Patients randomized into the Dexmedetomidine group (D) received, in addition to the mixture, 1mcg/kg Dexmedetomidine and the Epinephrine (E) group received 200mcg in the mixture. The primary outcome was time to first rescue analgesia as a surrogate for duration of analgesia and secondary outcomes were NRS pain scores up to 24 hours and opioid consumption.

The time to first rescue analgesia was not significantly different between Epinephrine and dexmedetomidine groups, Mean and SD 18.45 ± 12.98 hours vs 16.63 ± 11.80 hours with a mean difference of 1.82 hours (95% CI −4.54 to 8.18 hours) and p value of 0.57. Pain scores at 4, 6, 12, 18 and 24 hours were comparable between groups. Mean NRS pain scores Epinephrine vs Dexmedetomidine groups were 1.03 vs 0.80 at 4 hours, 1.48 vs 3.03 at 6 hours, 3.97 vs 4.93 at 12 hours, 5.31 vs 6.18 and 6.59 v 6.12 at 24 hours. Opioid consumption was also not statistically significant between both groups at 6, 12 18, 24 hours (p values 0.18, 0.88, 0.09, 0.64 respectively).

Dexmedetomidine does not prolong the duration of knee motor sparing blocks when compared to Epinephrine for total knee arthroplasty. Pain scores and opioid consumption was also comparable in both groups. Further studies using higher dose of dexmedetomidine are warranted.

Introduction

Total knee arthroplasty (TKA) is associated with significant blood loss, for which blood transfusion might be necessary. The role of the tourniquet is controversial, though it is widely used by orthopedic surgeons. Its use was believed to be effective in decreasing intraoperative blood loss and creating a bloodless surgical field, which theoretically would facilitate the cementing technique and other surgical procedures. However, reactive blood flow reached its peak within five minutes after the tourniquet had been released. The tourniquet controls intraoperative blood loss, but cannot stop postoperative blood loss. Patients who were managed with a tourniquet during the operation often complained of thigh pain. This was possibly caused by the direct pressure of an inflated tourniquet on the nerves and local soft tissues. Limb swelling and increased soft tissue tension caused by reactive hyperperfusion after tourniquet deflation may also contribute to the wound pain. The aim of our study is to investigate the effect of tourniquet on blood loss and soft tissue damage in TKA.