Effect of perioperative multimodal analgesia protocol on pain scores and recovery in dogs undergoing cruciate ligament repair

Introduction

The anterior cruciate ligament (cranial cruciate ligament in veterinary nomenclature) is the most commonly injured ligament in dogs, with TPLO now established as the gold-standard surgical correction for medium and large breeds [1,2] . The procedure involves an osteotomy of the proximal tibia, generating substantial perioperative pain that standard single-agent opioid protocols often fail to control adequately [3] . The multimodal analgesia concept-targeting multiple points in the nociceptive pathway simultaneously-has become standard of care in human orthopaedic surgery but remains inconsistently applied in veterinary practice [4] . The rationale for combining agents is pharmacological synergy: opioids act centrally, NSAIDs reduce peripheral inflammation, local anaesthetics block neural transmission at the surgical site, NMDA receptor modulators (ketamine) or gabapentinoids address central sensitisation, and constant-rate infusions maintain steady plasma levels [5,6] . Published veterinary trials have examined individual components but rarely tested a comprehensive multi-agent protocol against standard care in a controlled design. This research directly compared a full multimodal protocol with standard analgesia in dogs undergoing TPLO, using validated pain assessment and functional recovery endpoints.

Materials and Methods

Materials

Thirty-two client-owned dogs (16 per group) scheduled for unilateral TPLO at the UNMSM Veterinary Teaching Hospital between March and October 2023 were enrolled. Inclusion criteria: body weight 20-45 kg, age 2-8 years, ASA I-II status, unilateral cranial cruciate ligament rupture confirmed by drawer sign and tibial thrust. Exclusion: concurrent orthopaedic conditions, prior stifle surgery, hepatic/renal disease, chronic pain medication. The UNMSM Animal Ethics Committee approved the protocol (UNMSM-FMV-CE-2023-019). Randomisation used sealed envelopes.

Methods

The standard group (STD) received pre-operative methadone 0.3 mg/kg IM and meloxicam 0.2 mg/kg SC, with postoperative methadone 0.2 mg/kg IM every 6 hours for 48 hours. The multimodal group (MMA) received the same preoperative agents plus intra-operative fentanyl CRI (5 µg/kg/h) and lidocaine CRI (50 µg/kg/min), intra-articular bupivacaine 0.5% (0.5 mL/kg) at closure, and post-operative methadone 0.2 mg/kg every 4 hours plus gabapentin 10 mg/kg PO BID [7,8] . All dogs received standardised general anaesthesia (propofol induction, isoflurane maintenance). Pain was assessed by a blinded observer using the Glasgow CMPS-SF at pre-op, 2, 4, 8, 12, 24, and 48 hours post-surgery [9] . Rescue analgesia (morphine 0.5 mg/kg IM) was administered if CMPS-SF ≥ 6/24. Functional recovery was measured by time to first unassisted weight-bearing. Data were analysed by repeated-measures ANOVA and Fisher's exact test (p < 0.05). Pain scores in the MMA group remained below the rescue threshold (≥6) at all time points, whereas the STD group exceeded the threshold in seven of 16 dogs within the first 8 hours. The greatest between-group difference occurred at 2 hours post-surgery, coinciding with the residual effect of intra-operative CRI and intra-articular bupivacaine. By 48 hours, MMA scores had essentially normalised (0.6 ± 0.4) while STD scores remained mildly elevated (2.1 ± 0.8).

Results

Discussion

The 32% absolute reduction in pain scores at 2 hours and 40% faster weight-bearing in the MMA group demonstrate clinically meaningful benefits of combining multiple analgesic mechanisms for TPLO. Intra-articular bupivacaine likely contributed most to early post-operative pain control by blocking nociceptive input directly at the surgical site, a finding consistent with human total knee arthroplasty literature [10,11] . Gabapentin's contribution to central sensitisation prevention likely explains the sustained pain score advantage at 24-48 hours, well beyond local anaesthetic duration [12] . The higher sedation scores in the MMA group at 4 hours represent the expected trade-off of more aggressive analgesia, though scores normalised by 8 hours and no dog required clinical intervention for excessive sedation. Rescue analgesia rates (12.5% vs 43.8%) translate directly into welfare improvement and align with the principle that preventing pain is more effective than treating established pain [13] .

Limitations

Sample size (16 per group) limits detection of rare adverse events. Single-centre design and standardised breed/weight range may limit generalisability. The blinded observer could not be blinded to sedation differences. Long-term functional outcomes (limb use at 6-8 weeks) were not assessed.

Conclusion

This research demonstrates that a multimodal protocol combining opioid, NSAID, local anaesthetic, and gabapentinoid agents produces significantly better pain control and faster functional recovery after TPLO compared to standard opioid-NSAID analgesia. The 40% reduction in time to weight-bearing and three-fold reduction in rescue analgesia requirements provide strong evidence for multimodal protocol adoption. Remaining questions include cost-effectiveness analysis and whether the protocol can be simplified without losing efficacy.

Acknowledgement

Acknowledgements Institutional SupportThe UNMSM Veterinary Teaching Hospital provided surgical and anaesthetic facilities.

References

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