There are many potential benefits for using ribs as anchors (Table 48.1), the first of which is that the rib attachments may allow for motion preservation. The ribs are attached to the spine via the costotransverse joints (neck of rib to anterior portion of transverse process) and the costovertebral joints (head of rib to vertebral body). The costovertebral joints constitute a series of gliding or arthrodial joints formed by the articulation of the rib head with the facet on the contiguous vertebrae. Ribs 1, 10, 11, and 12 articulate with single vertebral bodies; the remaining ribs attach to two vertebrae [4] (Fig. 48.2a, b). These joints permit a gliding motion. During normal respiration, there is just over 10° of bucket-handle motion of the ribs relative to the spine [5]. In addition, the interface of a hook on the rib is not rigid and allows for some “slop.” Yamaguchi et al. reviewed a series of 176 patients treated with growing rods. In this series, proximal rib anchors were protective against rod breakage with a 77 % decreased incidence compared to proximal spine anchors [6]. Additionally, rib hooks may have an advantage in preventing anchor failure. Akbarnia et al. performed the first study to evaluate the properties of rib hooks used as an upper growing rod foundation in a porcine cadaver model [7]. They showed that rib hooks had a significantly higher load to failure than transverse process–lamina hook pairs and lamina hook–lamina hook pairs. Rib hooks had a higher load to failure than pedicle screws but this was not significant.

In contrast, traditional growing rods attached to the spine permit little motion of the vertebrae within the construct. As with any diarthrodial joint, prolonged immobilization decreases motion and can lead to spontaneous fusion. It is a common experience upon converting growing rods to a final fusion construct to discover spontaneous fusion of most, if not all, of the vertebrae within the construct. Sankar et al. substantiated this theory demonstrating in patients treated with dual growing rods that over time there was less increase in T1 to S1 distance with each subsequent growing rod lengthening [8]. This “law of diminishing returns” is a particular concern when growing rods are placed in young children, i.e., if dual rods are placed in a 2-year-old, the spine may be fused by age 7. In theory, the use of the ribs for anchor points will permit motion between vertebrae and prevent or delay spontaneous fusion. This technique is too new to have adequately tested this theory.

Another advantage of using ribs as anchors is to stay out of the spine and preserve a virgin spine for future surgeries. While traditional growing rods aim for a fusion at the top of the construct, methods that attempt nonfusion, such as Luque-Trolley (sublaminar wires and rods without fusion), have been shown to cause fusion in 100 % of patients in one series [9]. Fusion in the upper thoracic spine (T1–T3) in young children is particularly harmful to long-term pulmonary function, so avoiding fusion in this region may be an important benefit of this technique [10].

It has been shown that children with thoracic insufficiency are nutritionally depleted, with 79 % being below the fifth percentile for weight [11]. Soft tissue coverage of traditional spine implants can be challenging in this population. A further advantage of rib anchors is that they tend to have good soft tissue coverage, as they are located deep to the rhomboids and trapezius, in a valley between the more prominent spine and scapula (Fig. 48.3).

A significant practical advantage of using traditional spine implants on ribs rather than VEPTR is that no special equipment is needed. Hooks that fit the ribs are readily available on all spine implant systems. There are, thus, no special equipment needs and no special training needed for the surgeon or operating room staff. In addition, there is no need for institutional or research approval as traditional spine implant hooks are FDA approved. A particular advantage over the original VEPTR design is that load sharing over multiple ribs is quite simple (Fig. 48.4).