Predicting, Understanding and Speeding Recovery After TKA

The investigators propose a two-site, longitudinal, double-blind, randomized clinical
intervention study to examine three specific aims:

Aim 1: Characterize the dynamic pain experience, activity, and cognitive response after TKA
and determine patterns of recovery in these domains

Aim 2: Test whether gabapentin alters time course of recovery after TKA in a manner dependent
on its interaction with pre-drug pupil diameter and preferred style in the
catastrophizing-optimism dimension

Aim 3: Test whether gabapentin increases pupil diameter in patients undergoing TKA who are on
high dose opioids preoperatively and to examine whether opioid use moderates the associations
in Aim 1

Primary Hypothesis: Novel variance beyond established associations in recovery from pain
following TKA surgery is accounted for by the interaction between pupil diameter and
Cognitive-Affective (C-A) state, and this interaction predicts efficacy of gabapentin to
speed recovery.

Key secondary hypotheses: Disability, impulsivity, and attentional deficits recover after TKA
surgery follow a log of time pattern, and are predicted by C-A state and its interaction with
pupil diameter. Gabapentin increases resting pupil diameter in patients scheduled for TKA who
are receiving high doses of opioids.

Inclusion Criteria:

- Adults scheduled for elective total knee replacement

- American Society of Anesthesiologists physical status 1-3

- Participants must be able to read and write English

Exclusion Criteria:

- Inability to complete questionnaires

- Pregnancy

- Litigation or workers compensation related to joint surgery

- For 250 subjects in primary analysis - taking < 100 mg morphine equivalents/day. For
50 subjects to test gabapentin's effect on pupil diameter - taking >100 mg morphine
equivalents/day

- history of Raynaud's disease of the feet

- suffering from a psychotic disorder or a recent psychiatric hospitalization

- history of eye surgery or topical eye medications that would render pupillometry
unreliable or would directly affect pupil diameter.

- any disorder that would affect pupil responsivity or prevent accuracy of pupillometry
such as movement disorders