We found an increased risk of POP ≥ 2 after POP surgery in women with LAM trauma and reduced risk for symptoms after surgery for women with absent to weak pelvic floor contraction. Preoperative POP ≥ 3 was associated with an increased risk of POP ≥ 2 in any compartment after surgery.
Increased risk of POP ≥ 2 after surgery in women with LAM trauma is in line with previous studies on risk factors for recurrence after POP surgery. A meta-analysis by Friedman et al. found OR 2.76 (2.17–3.51) for levator avulsion as a predictor of recurrence, which corresponds well with our finding (OR 2.1 (1.1–4.1) . Increased risk of prolapse in a new compartment for women with LAM trauma is similar to other studies on women after POP surgery [19, 20]. A study by Oversand et al. on outcomes after POP surgery in the anterior compartment, however, showed no association with LAM trauma . This study differs from the present study because all women underwent a Manchester procedure (anterior colporrhaphy, cervical amputation and posterior colpoperineorrhaphy), whereas women in our study had different procedures and only 15% underwent surgery with a Manchester procedure. Our study was not powered for a sub-analysis on the Manchester procedure.
The term contraction is disputed in the academic community as it is often used as a synonym for strength or contractility. One problem with using absolute change in diameter between rest and contraction is that this does not take into account the reduced potential for change in women with a small hiatus at rest. By using proportional change in this study, differences in resting hiatal dimensions are accounted for. This measure correlates well with other methods used for assessment of pelvic floor contraction, such as palpation and vaginal manometry, and it is reliable [13, 22].
No impact of absent to weak pelvic floor contraction on anatomical outcome also coincides with a previous study of anatomical recurrence . We found that absent to weak contraction was associated with reduced risk of reporting bulge sensation after surgery and of a composite outcome of anatomical failure and symptoms (borderline significant). The women with normal to strong contraction were younger than women with absent to weak contraction. Younger women with pelvic floor disorders are more likely to report symptoms . Also, young women are usually more physically active, including heavy physical work, and this may provoke symptoms .
Trauma to the pudendal nerve may cause impairment of both motor and sensory innervation in the pelvis [25, 26]. This provides a possible explanation for why women with impaired pelvic floor contraction at the same time could have reduced sensibility and thereby higher thresholds for reporting a bulge sensation in our study, but this needs further investigation. A short follow-up (6 months) may influence the results, and symptomatic prolapse may manifest later after surgery . The healing process may not be complete, and sensation may be temporary reduced after surgery . Women with absent to weak contraction had more previous POP surgery (borderline significant), which may further reduce the sensibility.
Levator ani muscle trauma and absent to weak pelvic floor contraction seem to increase the risk of development of POP in a new compartment. However, the numbers were small with wide confidence intervals and further studies are needed to confirm this result.
One strength of this study was the use of validated methods to evaluate LAM trauma, anatomy and symptoms after POP surgery. Our diverse population makes the results generalisable to clinical practice. However, the construction of the cohort may introduce a selection bias as we combined women from a randomised controlled trial with women declining participation.
The definition of anatomical recurrence (POP stage ≥ 2) in this study can be debated, as a POP stage 2 in the anterior compartment is often asymptomatic, whereas a stage 1 in the mid compartment can be symptomatic .
Inclusion of both primary and recurrent POP and surgery in different compartments can represent limitations of our study because anterior and posterior POP may have different aetiologies. There was also diversity in the surgical procedures, and the study sample size made sub-analyses for different procedures and compartments impossible. All women were instructed on how to contract the pelvic floor correctly. Knowledge of pelvic floor anatomy and contraction may have made these women perform better than a general patient population.
This research adds knowledge about the impact of LAM trauma and contraction on anatomical and symptomatic surgical outcomes. We suggest that evaluation of pelvic floor muscle trauma and ability to contract should be performed as a part of a standard gynaecological examination. Identification of women with LAM trauma can contribute to early prevention of POP development through pelvic floor muscle training  and postpone surgery. In addition, assessment of LAM trauma and contraction prior to POP surgery can influence choice of procedure and follow-up after surgery. The impact of sensitivity and function in women with prolapse needs further evaluation.
In conclusion, we found an increased risk of overall anatomical POP ≥ 2 after surgery in women with LAM trauma, but not an increased risk of bulge sensation. Women with absent to weak contraction had a reduced risk of bulge sensation after surgery.