Delivery workers have one of the highest rates of musculoskeletal injury compared to other occupations. The television show King of Queens might portray Doug Heffernan as a lighthearted, rarely debilitated delivery worker, but in reality, this occupation is physically and mentally demanding, with injuries comparable to those experienced by professional athletes. 

The unique biomechanical challenges of this occupation put these workers at significant risk for a host of musculoskeletal complaints, including injuries to the shoulders, neck, back, head, and knees. 

Delivery workers have several work-related challenges: long periods of seated driving, repetitive lifting and bending, heavy lifting, reaching, jumping out of vehicles, going up and down stairs, opening and shutting cargo doors, and being on a hectic time schedule. Poor posture during these activities adds to the risk of injury.

Of course, there are particularly high rates of injury and pain in the neck and back, but shoulders, upper extremities, and lower extremities are also at risk. My previous articles on musicians (January/February 2012), dentists (March/April 2012), and hotel workers (May/June 2012) covered shoulder injuries; here I focus on low-back and knee problems. 

Massage treatment is very effective for addressing these disorders, but more importantly, massage helps relieve the cumulative stresses that can lead to more debilitating conditions.

Biomechanics of Low-Back Muscle Injury

The primary action of the torso in lifting is lumbar extension, mainly with the lumbar extensor muscles. Other muscles contribute to lumbar extension, but the main extension force is generated by the erector spinae muscle group. Improper lifting routinely puts stress on these muscles, which leads to muscular injuries such as strain, spasm, or chronic hypertonicity. 

One of the reasons back injuries are so frequent is that the lumbar muscles are in a poor mechanical position for lifting heavy loads. In relation to the lumbar spine, the lumbar muscles have a poor “moment arm,” which is the force used to produce a motion multiplied by the distance of that force from the axis of rotation. In essence, the closer a muscle is to the joint’s axis of rotation, the less capable it is of producing significant force. The lumbar extensor muscles lie directly along the spine (very close to their axis of rotation) and are in a poor mechanical position for lifting activities, which can lead to muscle fatigue and injury (Image 1).

The strong lumbodorsal fascia helps the lumbar muscles by lending tensile power from the other muscles connected to it, including the latissimus dorsi, gluteus maximus, transverse abdominis, and abdominal obliques. Their mechanical role is to produce tension on the lumbodorsal fascia, which then supports the lumbar muscles in lifting actions. Consequently, it is very important to address these other muscles when treating lumbar pain. 

Poor sitting postures and improper lifting techniques can produce radiating back pain. Long periods of isometric muscle contractions from sitting lead to chronic tightness, pain, and myofascial trigger points in the lumbar erector spinae muscle group. These chronic contractions, exacerbated by heavy lifting, can lead to facet joint dysfunction and disc pathology. 

Facet Joint Dysfunction

The facet joints of the spine (zygapophysial joints), located on the posterior aspect of the vertebral arch, are the only bone-to-bone contact surface of adjacent vertebra (Image 2). Facet joint dysfunctions occur as a result of compression forces on the spine. When the disc loses height from compression, the facet joints compress together, irritating the adjacent contact surfaces of each vertebra. 

Even slight overloading of the back with the spine in extension can put excessive loads on the facet joints. Those with exaggerated lumbar lordosis have increased pressure on these joints. 

Disc Pathology

Most disc herniations occur as a result of moderate compressive loads endured over time. Disc herniations develop in this worker population because of chronic compressive forces (sitting) and heavy lifting that places significant compressive loads on the discs, producing disc pathology. 

The disc is thicker on the anterior portion than the posterior in order to maintain the normal lordotic curvature of the spine (Image 3). When the spine is flexed, as it is during lifting activities, there is greater compression on the anterior aspect of the annulus fibrosis, while the posterior annulus is overstretched. The tensile forces on the posterior annulus, where it is overstretched, lead to weakening and eventual disc degeneration and herniation. 

Knee Biomechanics and Pathology

Delivery drivers also put an enormous demand on their knees. Constant bending of the leg with weight places adverse wear on the patella and its tendon, the anterior cruciate ligament (ACL), as well as the meniscus. Repetitive loads on the knee extensor structures make them susceptible to injury. 

The patella functions to increase the power of the quadriceps, acting as a fulcrum during extension, and is embedded within the tendon of the quadriceps muscles (Image 4). Consequently, there is a great deal of tensile (pulling) force on the patellar tendon with knee extension during lifting. 

As the knee extends, the patella moves in a superior direction. Sometimes the forces on the tendon are not equal; most commonly there is a greater pull on the lateral side compared to the medial side of the patella. The imbalanced pull can produce a patellar tracking disorder, a primary cause of anterior knee pain.

Delivery workers also sustain chronic overuse tendon pathologies such as patellar tendinosis, which is chronic overload on the tendon but not necessarily a tracking disorder. Patellar tendinosis involves chronic degeneration of the collagen matrix within the patellar tendon. Unfortunately, tendinosis heals slowly, and people often go back to activities long before they are at optimum function, thereby aggravating and prolonging the existing injury.

ACL and meniscus pathology are also common. Powerful contractions of the quadriceps, as during lifting and bending, produce a high tensile force on the ACL, which can, with repetition, cause gradual breakdown and sprain injury to the ACL.

The ACL can be injured with simultaneous bending and twisting movements, which are common for delivery drivers. Rotational stress to the knee puts the ACL in a compromised position, a common mechanism of injury, and can seriously stress the medial collateral ligament (MCL) and the medial meniscus. In fact, these three structures are so frequently injured together that they are known as the “terrible triad.”

The ACL and medial meniscus are structures deep within the knee and inaccessible to massage treatment. Conditions involving these two structures should be treated by an orthopedist. The MCL, however, is accessible for massage treatment and responds well to deep-friction massage, along with other movement methods used in physical therapy. 

Evaluation and Treatment Considerations
Low Back

A variety of treatment techniques are valuable for both injury prevention and treating existing conditions in delivery workers. Appropriate treatment is dictated by which structures are responsible for producing the pain. Consequently, assessment and evaluation are of key importance. Low-back pain assessment can be challenging, but there are some simple key principles to help clarify your client’s condition.

Reports of sharp, shooting pain sensations, especially down the lower extremity, are likely if there is a disc pressing on lumbar nerve roots. Suspicion of neurological involvement can be further examined with special orthopedic tests, such as the straight leg raise test. This is one of the most commonly used evaluation procedures for identifying neurological involvement of the lumbar nerve roots.

Palpation will clarify muscular injury, such as myofascial trigger points, hypertonicity, or muscle strain. Developed palpation skills combined with knowledge of anatomy and relevant structures help determine which tissues might be the cause of pain (if palpation reproduces the pain). Note that pain referred to other regions from palpation of lumbar muscles is frequently an indication of myofascial trigger points. Pain that mimics the exact sensation the client reports strongly suggests involvement of local muscles as the primary cause. Further validation of which soft tissues are injured can be aided by combining information from active, passive, and manual resistive tests.

Myofascial techniques gently pull and elongate the connective tissues of the superficial fascia, decreasing tightness in the deeper muscles. Initial relaxation allows these deeper muscles to be treated with more specific techniques. Myofascial methods also reveal the areas of greater resistance and muscle tightness that need attention.

Numerous techniques can be used to address low-back tightness; however, it is crucial to get to the often-ignored, deeper intrinsic spinal muscles. Your technique needs to be deep and specific to get to these muscles. Make sure you are familiar with the anatomical structures in this area and recognize where you can put pressure on muscles without adversely compressing bony prominences such as the transverse or spinous processes of the lumbar vertebra. 

The deep, intrinsic spinal muscles frequently hold myofascial trigger points. Static compression and deep stripping techniques will address chronic tightness and neutralize trigger points (Image 5). If the contact surface is too broad (e.g., using the palm, open hand, or flat fingertips), you will not accurately get at the very deep muscles, such as the lumbar multifidus. It is wise to use a broader contact surface first, but make sure to eventually get into these areas with a small contact surface as well. Stripping techniques are particularly valuable in encouraging elongation and relaxing the shortened sarcomeres that result from overload. 

Knee 

Anterior knee pain can sometimes be a bit misleading, so accurate assessment is important. Most of the involved structures are superficial, so palpation plays a primary role in evaluating dysfunction in the knee extensor complex. 

Anterior knee pain prominently reproduced when pressure is applied to the infrapatellar tendon is strongly indicative of patellar tendinosis. The chronic collagen degeneration of tendinosis takes a long time to heal, but should be addressed with a comprehensive treatment approach, including reducing tightness in the quadriceps along with deep-friction techniques directly on the tendon. Working the quadriceps reduces the pull on the tendon. The primary function of friction techniques to the tendon is stimulating fibroblast proliferation, which helps heal collagen degeneration.

Patellar tracking disorders can be challenging to identify, but frequently involve significant tenderness in the retinaculum around the knee, which is indicative of imbalanced forces pulling on the retinacular tissues. The primary massage methods for patellar tracking disorders emphasize reducing the excessive pulling load of the quadriceps muscle group on the patellar tendon. This is accomplished by treating the quadriceps with deep, compressive effleurage, sweeping cross-fiber techniques, and longitudinal stripping methods. Stretching is particularly valuable to encourage flexibility and elongation in the quadriceps.

It is crucial to address the patellar retinaculum as well as the quadriceps group. The patellar retinaculum is an expanse of connective tissue that extends from the distal quadriceps muscle fibers into the patellar tendon and its associated attachment at the tibial tuberosity. The retinaculum is richly innervated, so it is a likely source of anterior knee pain when overstressed.

An excellent way to address the patellar retinaculum and patellar tendon is with active engagement methods. Because the quadriceps are a dense muscle group, particularly in certain individuals, common treatment methods may not provide adequate force to access the deeper tissues. Active engagement methods produce effective results because of the additional force involved in the treatment technique.

Massage as Solution

Cumulative effects and high physical demands are exaggerated with delivery workers. However, numerous other activities pose similar biomechanical challenges for the body. As always, proper assessment and evaluation are key factors before attempting any treatment approach. Armed with a good understanding of biomechanical relationships in these regions and the physiological impact of our treatments, massage therapists are in an excellent position to offer great help to this worker population.